Limitations of using micro-computed tomography to predict bone-implant contact and mechanical fixation.

Fixation of metallic implants to bone through osseointegration is important in orthopaedics and dentistry. Model systems for studying this phenomenon would benefit from a non-destructive imaging modality so that mechanical and morphological endpoints can more readily be examined in the same specimens. The purpose of this study was to assess the utility of an automated microcomputed tomography (µCT) program for predicting bone-implant contact (BIC) and mechanical fixation strength in a rat model. Femurs in which 1.5-mm-diameter titanium implants had been in place for 4 weeks were either embedded in polymethylmethacrylate (PMMA) for preparation of 1-mm-thick cross-sectional slabs (16 femurs: 32 slabs) or were used for mechanical implant pull-out testing (n= 18 femurs). All samples were scanned by µCT at 70 kVp with 16 µm voxels and assessed by the manufacturer's software for assessing 'osseointegration volume per total volume' (OV/TV). OV/TV measures bone volume per total volume (BV/TV) in a 3-voxel-thick ring that by default excludes the 3 voxels immediately adjacent to the implant to avoid metal-induced artefacts. The plastic-embedded samples were also analysed by backscatter scanning electron microscopy (bSEM) to provide a direct comparison of OV/TV with a well-accepted technique for BIC. In µCT images in which the implant was directly embedded within PMMA, there was a zone of elevated attenuation (>50% of the attenuation value used to segment bone from marrow) which extended 48 µm away from the implant surface. Comparison of the bSEM and µCT images showed high correlations for BV/TV measurements in areas not affected by metal-induced artefacts. In addition for bSEM images, we found that there were high correlations between peri-implant BV/TV within 12 µm of the implant surface and BIC (correlation coefficients ≥0.8, p < 0.05). OV/TV as measured on µCT images was not significantly correlated with BIC as measured on the corresponding bSEM images. However, OV/TV was significantly, but weakly, correlated with implant pull-out strength (r= 0.401, p= 0.049) and energy to failure (r= 0.435, p= 0.035). Thus, the need for the 48-µm-thick exclusion zone in the OV/TV program to avoid metal-induced artefacts with the scanner used in this study means that it is not possible to make bone measurements sufficiently close to the implant surface to obtain an accurate assessment of BIC. Current generation laboratory-based µCT scanners typically have voxel sizes of 6-8 µm or larger which will still not overcome this limitation. Thus, peri-implant bone measurements at these resolutions should only be used as a guide to predict implant fixation and should not be over-interpreted as a measurement of BIC. Newer generation laboratory-based µCT scanners have several improvements including better spatial resolution and X-ray sources and appear to have less severe metal-induced artefacts, but will need appropriate validation as they become available to researchers. Regardless of the µCT scanner being used, we recommend that detailed validation studies be performed for any study using metal implants because variation in the composition and geometry of the particular implants used may lead to different artefact patterns.

Effect of suckling during early lactation and changeover to machine milking on plasma oxytocin and cortisol levels and milking characteristics in Holstein cows.

Plasma concentrations of oxytocin and cortisol, and milk yield and flow rates, were compared in three primiparous cows and two cows in their second lactation during suckling and subsequent machine milking. After calving, cows suckled their calves for 3-4 weeks and then the experiment was carried out over 4 d. Blood samples were taken prior to, during and after suckling or evening machine milking (EMM) on day 1 of the experiment (the last day of suckling), day 2 (first EMM) and day 4 (third EMM). After weaning and rehousing, cows were machine milked twice daily. During the first EMM, average milk yield and flow rate in the second minute of milking were significantly lower (P < 0.05) than corresponding values for the other 2 d. Plasma oxytocin concentrations were lower during the first than during the third EMM (P < 0.001) and suckling (P < 0.001), and more oxytocin was released during the third EMM than during suckling (P < 0.01). Cortisol concentrations were higher during and after the first EMM than during the third EMM. Thus in cows sucked for several weeks after calving and then separated from their calves and rehoused we found a transient decrease in oxytocin release, milk yield and flow rates during the first machine milking.

Hepatitis B virus proteins expressed by recombinant vaccinia viruses: influence of preS2 sequence on expression surface and nucleocapsid proteins in human diploid cells.

Fifteen vaccinia virus (VV) recombinants derived from VV strains Praha, LIVP and DD (i.e. Dryvax Wyeth vaccine-derived) and expressing genes for S, preS2-S or c antigens of hepatitis B virus (HBV) were tested in monkey CV-1 cells and human diploid LEP cells. The production of infectious virus was found to be alike in all the recombinants and parental viruses as well. However, several recombinants produced markedly lesser amounts of S and preS2 antigens in LEP cells than in CV-1 cells. This reduction was independent of the parental virus used. There was, however, a relationship between the production of preS2 in CV-1 cells and the production of S and preS2 antigens in LEP cells; in general, recombinants efficiently inducing preS2 antigen formation in CV-1 cells produced markedly reduced amounts of S and preS2 antigens in LEP cells. Reduction of HBV antigen production in LEP cells was not apparent in recombinants expressing only S or c antigens of HBV, and the production of c antigen by double recombinants was not influenced by simultaneous expression of preS2 and S. The various recombinants also differed in the ratio of S:preS2 antigen formation. This difference seemed to be associated with the length of the untranslated leader sequence preceding preS2 but not with the parental virus or cell type used. The titers of antibodies against S and preS2 antigens induced in mice immunized with different recombinants differed markedly. The differences in the ratio of S:preS2 antigen production in vitro were not reflected in vivo by S:preS2 antibody ratio.

Vaccinia virus recombinants co-expressing hepatitis B virus surface and core antigens.

Using the Praha strain of vaccinia virus (VV) two double recombinant VVs expressing the surface and capsid HBV proteins (HBsAg and HBcAg) under the control of the P7.5 promoter were constructed. In the first construct the gene coding for HBsAg was inserted into the HindIII J fragment (TK gene) and the gene coding for HBcAg was inserted into the HindIII M fragment (host range, K1L gene) of the VV genome. To test whether the expression of the foreign genes was influenced by the insertion site, in the second construct their locations were inversely changed. When compared with single VV-HBV recombinants expressing either HBsAg or HBcAg, the double recombinants expressed in vitro approximately the same amounts of the respective antigens. The particles formed by either HBsAg or HBcAg expressed by recombinant viruses, were isolated and examined by electron microscopy. Particles composed of both HBsAg and HBcAg were not detected in cultures infected with one of the double recombinants. The residual virulence in 3-week-old mice of the single recombinants was not markedly altered by the insertion of the second gene. The immunogenicity in mice of both the single and double recombinants was comparable and was not influenced by the location of the HBV genes in VV genome, as revealed by antibodies developed against the respective antigens.

[Changes in oxytocin and cortisol levels in primiparous cows after changing from 21 days of suckling calves to machine milking]. / Zmeny hladiny oxytocínu a kortizolu u prvôstok po prechode z 21-dnového cicania tel'atami na strojové dojenie.

Four first-calvers of the Black-Pied breed with calves sucking their milk until day 21 of lactation were included in a trial. One suckler cow had four calves. The trial took place within five days which included days 20 and 21 in the first-calvers, that means the last two days with sucking calves (designated as day 1 and day 2 of trial-first and second calf sucking) and days 22 and 24, that means the first and third day after the cows were moved to a cowshed (designated as the third and fifth day of trial-first and third evening machine milking). The first-calvers were separated from the calves and moved to a cowshed at 8 o'clock a.m. on day 3 of trial (Tab. I). The responses to calf sucking were investigated after four-hour prevention of calves to approach the cows (12.00-16.00 p.m.). Blood was sampled with a catheter which was introduced into the vena jugularis a day before the trial outset. Blood samples for cortisol determination were taken in two-hour intervals (when the cows were moved to the cowshed twice in half-an-hour interval and once in an hour interval). Blood samplings were effectuated by day, before, during and after milking, or sucking. Machine milking was finished within 7 to 8 minutes. Two to four calves were intensively sucking a cow within the first 15 minutes, then sucking was irregular. Plasma samples were deep-frozen and stored at -20 degrees C until determinations were performed. Oxytocin and cortisol in the blood plasma were determined by radioassays. In the first evening machine milking (day 3) the second cow yielded 8.23 kg milk while on day 5 in the third milking it was 7.98 kg. The other first-calvers gave by 30-45% less milk on day 3 in comparison with evening milking on day 5 (Tab. II). A trend of the higher average values of oxytocin was observed in machine milking on day 5 of trial if compared with the values recorded during calf sucking, or the first milking (day 3), Fig. 1a, Tab. III. The mean oxytocin concentration during 7-minute milking (12.39 +/- 5.81 pg/ml) was significantly lower in the first-calvers on day 3 in comparison with the mean values recorded on day 5 (28.01 +/- 18.56 pg/ml; P < 0.001), or during sucking (18.32 +/- 7.15 pg/ml; P < 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)

[The effect of low temperatures on biochemical indicators in the blood of calves]. / Zmeny biochemických ukazovatel'ov krvi teliat pod vplyvom nízkych teplôt.

Twenty calves, heifers of the Holstein-Friesian breed and crossbreds with the Slovak Pied breed, were divided into two groups at the average age of 19 days. The trial group was kept outdoors in wooden hutches and the control group was housed in an insulated building. Blood was sampled at the age of 20, 33, 48 and 60 days at the outdoor temperatures of 3 degrees C, -2 degrees C, -5 degrees C and -8 degrees C. The calves kept in hutches where temperatures were always lower than in the insulated calf-house had the higher level of nonesterified fatty acids in all observations. The largest, highly significant difference was determined at the age of 60 days at the outdoor temperature of -8 degrees C (271 mumol/l vs. 224 mumol/l), and the significance of differences was also observed in the first and third blood samplings at the temperatures of 3 degrees C and -5 degrees C. The differences were highly significant in the first group between the first and fourth, and second and fourth samplings. In the calves kept in the insulated building the difference was significant between the first and fourth observation because the content of free fatty acids was also gradually increasing in this case (Tab. I). Glycaemia values were also higher in the calves kept in hutches (Tab. II). The most noticeable (significant) difference was determined at the age of 48 days at the outdoor temperature of -5 degrees C (4.3 mmol/l vs. 3.9 mmol/l). Significant differences within the group were recorded only in calves from the trial group kept in hutches. Insulin concentrations increased gradually with the older age of animals (Tab. II). At the age of 20 days the values were identical in fact in both groups and the highest concentrations were recorded at the age of 60 days. The differences between the groups were not significant, the largest difference was observed at the end of milk feeding period at the age of 60 days (19 microUI/l in calves from hutches and 15.6 microUI/l in calves from the insulated building). Triiodothyronine concentrations decreased from the starting values of 0.8 nmol/l and 0.76 nmol/l in both groups at the age of 33 days to the values of 0.61 and 0.62 nmol/l.(ABSTRACT TRUNCATED AT 400 WORDS)

[The effect of high-dose ultraviolet irradiation on sodium, calcium and aldosterone in the blood of calves]. / Pôsobenie nadmerného ultrafialového ziarenia na sodík, vápnik a aldosteron v plazme teliat.

Five Holstein-Friesian calves, from one sire, with prevalent black hair coat pigmentation were used in the experiment. The mean age was 33 days and the mean live weight 51 kg. The animals were exposed free running without interruption for 12 hours to an artificial ultraviolet light in the range of 280-320 nm. The mean doses of radiation was 179.10(-10) J/h/m. One-spot high-pressure mercury discharge lamps Tesla RVK 400 W were used as a radiation source. The dose rate was estimated from measurements by a spectral photometer with filter UG 2 for absorbtion of visible light located at the height of the back of standing calf. Blood samples were collected immediately before the beginning of treatment and after 5, 12, 24, 48 and 72 hours. The blood plasma aldosterone was measured by radioimmunoassays, the levels of sodium, potassium and calcium in blood plasma by flame spectrophotometry. Double classification variance analysis and evaluation according to the Snedecor F-test, the contrast effect test according to Duncan and regression analysis were used for statistical evaluation. Compared to the first sampling, sodium increased significantly after 5 and 12 hours of exposure (Tab. I) to 138.1 and 138.3 mmol/l, respectively. In the subsequent samplings this trend continued up to 72 hours from the beginning of irradiation (140.5 mmol/l). The potassium level did not change statistically significantly. Owing to an excessive irradiation, the calcium concentration increased significantly. The greatest increase occurred after 12 hours of irradiation (from 2.29 mmol/l to 2.61 mmol/l) and after 36 hours from the end of irradiation (2.70 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)

[Relation between milk production and biochemical indicators in high- and low-producing cows]. / Vztahy mliekovej úzitkovosti a biochemických ukazovatel'ov u vysoko a menej úzitkových kráv.

23 cows of the Holstein-Friesian breed during second lactation were used in the experiment. All animals were housed in one stable with tying. The blood was collected from each cow four times during first to third, fourth to sixth, seventh to ninth and above nine months of lactation. After 305 days of lactation, the milk cows were classified as with high (n = 14) and lower performance (n = 9), the limit value was 5000 kg of milk. The difference in milk production between groups was highly significant even during the period of the first 90 days (501 kg) and this difference increased for 305 days of lactation to 1538 kg (Tab. I); the dairy cows with high performance produced 6162 kg of milk per 305 days and that with the lower performance gave 4624 kg during the same period. Another significant differences occurred in the fat contents per kg and in the amount of milk converted on 4% fat content. During the first stage of lactation a slightly higher haemoglobine level was found in cows with high performance, the opposing results were obtained in another studies (Tab. II), the highest difference was recorded in the course of 7th to 9th month. The level of total protein was, except 7th to 9th month, always higher in cows of the first group. The difference was significant at the beginning of lactation. Insulin concentration (INS) exhibited identical tendency for the whole lactation--dairy cows with high milk production exhibited lower values, significant differences were recorded in the first observation at the beginning of lactation and in the period above 9 months. Similarly as in case of insulin, it is also in hormones of thyroid gland, the cows with high milk capacity had the lower values (Tab. III). The highest differences in triiodothyronine (T3) concentration were recorded in the second half of lactation, significance ranged from 7th to 9th month of lactation. In thyroxine content (T4), marked differences were recorded during the first and last observations, the difference was highly statistically significant during the seventh to ninth month of lactation. The levels of cyclic adenosine monophosphate (AMP) were higher for the whole experiment in animals with lower milk production. Tab. IV gives the correlation coefficient of different parameters between periods under study. Almost all parameters are in a close positive relation, the closest dependences were observed between second, third and fourth periods in hormones of thyreoidea. The most significances were recorded in adenosine monophosphate, thus confirming its stability of minimum variance between observations.(ABSTRACT TRUNCATED AT 400 WORDS)

Estimation of cold stress effect on dairy cows.

Twelve crossbred heifers (Slovak Spotted x Holstein-Friesian) were housed in an open, uninsulated barn with straw bedding and a concrete-floored yard. Minimum temperatures inside the barn were as low as -19 degrees C. The average milk yield decreased as the temperatures approached these minima. Compared with the temperature conditions, the feed intake and blood levels of glucose and free fatty acids increased. The level of sodium declined significantly during the second cold period. Correlations and regressions between milk yield and biochemical parameters were calculated, and the results indicate that the concentrations of free fatty acids, cholesterol, and triiodothyronine and the haematocrit values may serve to predict milk production during periods of cold stress, or in lactations of 305 days.

[The health status and metabolic indicators in calves fed colostrum and first milk preserved with potassium sorbate and milk replacements]. / Zdravotný stav a metabolické ukazovatele u teliat napájaných mledzivom a nezrelým mliekom konzervovaným sorbanom draselným a mliecnou krmnou zmesou.

The aim of the experiments was to investigate the effects of the preservation of colostrum and unripe milk with potassium sorbate at a concentration of 0.5% and of its storage for three to five days at normal environmental temperatures on the calf health condition. A set of 30 calves divided into two groups was included in the trial. Calves belonging to the experimental group were fed preserved colostrum and unripe milk from day 9 to day 30 of their life (the first experimental period), and from day 31 to day 50 (the second experimental period) milk replacer. Calves belonging to the control group were fed milk replacer from day 9 to day 50 of their life. One calf from the experimental group died from a respiratory disease. In the control group, one calf died and another had to be slaughtered; in both cases digestive tract diseases were diagnosed. The number of calves which had to be treated medically was also lower in the experimental group--in the calves fed preserved colostrum--one case of periodic tympany was recorded in comparison with four cases in the control group. When haematological and biochemical characteristics were examined, significantly lower haemoglobin levels were found in experimental calves at the end of the first experimental period (105.4 g.l-1 when compared with 112 g.l-1 in the control group) and significantly higher values of proteinaemia were found in the blood plasma of these calves at the same period (59.6 g.l-1 and 53.8 g.l-1, respectively). Similar differences were also found during a single haematological and biochemical examination.

[The hormonal response in bulls to the administration of zeranol and rumensin]. / Hormonálna reakcia býkov na podávanie zeranolu a rumensinu.

The objective of the study was to investigate the influence of the growth stimulators Ralgro zeranol and Rumensin on changes in concentrations of certain hormones in the blood of beef bulls. In the first experiment 21 bulls were investigated which were divided into three groups. The first group was control, the second was administered the Ralgro stimulator (3X) and the third the Ralgro and Rumensin stimulators. In the second experiment there were 12 bulls. The animals in the test group were implanted Ralgro five times during the fattening period. Alternate changes, mostly insignificant, were recorded between the groups in the concentration of triiodothyronine and cyclic adenosine phosphate. Thyroxine concentrations were reduced during all investigations of the first and second experiments in the animals stimulated by the Ralgro preparation. A significant increase was recorded in the bulls at the age of 14.3 months in the second experiment (62.8 nmol.l-1, in comparison with 56.9 nmol.l-1). In both experiments an identical trend of insulin content was observed--in seven out of the total number of eight observations the animals treated with the Ralgro preparation had statistically insignificantly higher values. The largest differences were recorded at the age of 11.1 and 14.3 months in the second experiment (3.9 microIU.ml-1 and 3.6 microIU.ml-1). Significant differences were observed in testosterone concentrations in the second bulls of the test group were lower by 1.9+ nmol.l-1 and 3.4++ nmol.l-1, respectively.

[The effect of excessive artificial UV radiation on the measurement of blood parameters and phagocytosis in calves]. / Einfluss der übermässigen künstlichen UV-Strahlung auf die Messgrössen des Blutbildes und auf die Phagozytose bei Kälbern.

5 calves of an age of 33 days were exposed to UV-light (280-320 nm) for a time of 12 hours. The mean dose of radiation was 179 x 10(-10) J/h x m-2. The results show slight influences of overdosed radiation on hemoglobin content of the blood, from 105.1 g/l to 102.6 g/l. The mean content of hemoglobin in erythrocytes decreased: 364 g/l to 347 g/l. The total leucocytes decreased from 7.74 x 10(9)/1 to 7.08 x 10(9)/1 after exposition of 5 hours. The exposition increased lymphocytes (55.6% to 66.0%) and decreased neutrophils (43.6% to 33.8%). The relationship of lymphocytes to neutrophils extended even after radiation time of only 5 hours from 1.45 to 2.04. The phagocytotic activity increased after 5 hours of exposition. To the end of exposition (60 hours after observation) a decrease was observed. A correlation between doses of radiation and hematological changes was found after 12 hours of radiation in lymphocyte counts (r = 0.878) and neutrophil counts (r = -0.824) as well as in the relation of lymphocytes to neutrophils counts (r = 0.941) and in the index of phagocytosis (r = 0.804).

[The effect of artificial ultraviolet light on biochemical indicators in calves]. / Vplyv umelého ultrafialového svetla na biochemické ukazovatele teliat.

Changes in the biochemical parameters of the blood serum of calves were studied after exposure to optimum doses of ultraviolet radiation. The calves were exposed to UV-light twice daily in three periods: 8, 9 and 10 days. Daily doses of 90, 130 and 180 mEr.h.m-2 were used in the first experiment, 120, 180 and 240 mEr.h.m-2 in the second experiment. As found, exposure to radiation in the individual periods increased total proteinaemia, the differences between the experimental and control groups being significant. Exposure to ultraviolet light induced an increase in the activity of the thyroid gland; at the end of the periods of UV-radiation the concentration of thyroxine in the experimental groups was significantly or highly significantly higher. The largest differences were recorded in the first trial (15 nmol per litre to 21.4 nmol per litre). No changes were detected by the evaluation of the activities of alkaline phosphatase, triiodothyronine, sodium, potassium and calcium and in the sodium: potassium ratio.

[Changes in biochemical indicators in dairy cows induced by extremely low temperatures]. / Zmeny biochemických ukazovatel'ov dojníc vyvolané extrémne nízkymi teplotami.

The objective of the experiment was to find out the effect of extremely low temperatures on the biochemical characteristics of the cows. Twenty-one dairy cows were used as the experimental material. The experimental group (n = 12) was kept loose in an open barn without thermal insulation and the control group (n = 9) was kept in an insulated cow-house. The winter season included two periods of extremely low temperatures: from the 3rd to the 21st of January 1985 the average minimum temperature in the open barn was -12.6 degrees C and the lowest temperature was -19 degrees C, and in the period from the 8th to the 20th of February 1985 the average minimum temperature was -13.1 degrees C and the lowest recorded temperature was also -19 degrees C. At the beginning of hypothermic stress, the concentration of non-esterified acids and total proteins increased in the cows of the experimental group; potassiaemia was decreased in this group. Cholesterolaemia and glycaemia increased during the long-continued exposure to low temperatures. The activity of the thyroid gland was increased at all measurements.

[The effect of extreme temperatures on hematologic and biochemical indicators in heifers]. / Vplyv extrémnych teplôt prostredia na hematologické a biochemické ukazovatele u jalovíc.

The study was aimed at finding the effect of low and high temperatures on some biochemical parameters in heifers. Thirty half-sister heifers were used as the experimental material. The animals were divided into two groups. The experimental group including 16 heifers was kept loose on deep litter in an open barn with no thermal insulation. The control heifers (n = 14) were kept in a thermally insulated house. Blood was collected at extreme temperatures: above 30 degrees C and below -5 degrees C. An insignificant decrease of haemoglobin and haematocrit was recorded in the blood collected at low and high temperatures from the heifers kept in the open barn; a reduction of cholesterolaemia and total lipaemia was recorded at high temperatures. High and low temperatures significantly increased the concentration of free amino acids; the differences between the experimental and control group being from 36 to 76 mumol per litre. The content of 3.5-cyclic adenosine monophosphate was increased insignificantly at extreme temperatures. Hyperglycaemia was recorded in the heifers at high temperatures and at the beginning of the winter season. At low temperatures the concentration of thyroxine was found to be increased in the blood of the experimental animals: 120 nmol per litre and 161 nmol per litre vs. 95 nmol and 116 nmol in the control group.

[The effect of prolonged movement restriction of dairy cows on biochemical parameters]. / Vplyv dlhodobého obmedzenia pohybu dojníc na biochemické ukazovatele.

In thirty-three dairy cows--first calves, the influence of hypokinesis on biochemical parameters was studied over three lactation periods. The cows of the experimental group (n = 15) were reared in steel cages enabling only minimum movement, whereas the control group (n = 18) was housed loosely. It was found out that the permanent movement restriction led to a statistically significant decrease in hemoglobin and hematocrit concentrations, as well as in aspartate aminotransferase activity. In comparison with the control group, a significant decrease was also observed in substances of the lipid group--cholesterol, triglycerides and total lipids. Similarly, thyroxin and total proteinemia were lower.

Prospective study on the relationship between cervical neoplasia and herpes simplex type-2 virus. II. Herpes simplex type-2 antibody presence in sera taken at enrollment.

Sera obtained at enrollment in the study from patients suffering from moderate to sever dysplasia (cervical intraepithelial neoplasia grade II), carcinoma in situ (cervical intraepithelial neoplasia grade III) and invasive carcinoma, or developing any of these conditions in the course of the prospective study, and from control subjects, were examined for herpes simplex type-2 (HSV-2) antibody presence. The controls were matched with the patients by age, age at first intercourse, number of sexual partners, smoking habits and history of diathermoelectrocoagulation of the ectopic epithelium and transformation zone of cervix. Only those subjects were selected as controls who remained free of pathological colposcopical and cytological findings throughout the observation period, i.e. for at least 4 years after their serum sample was obtained. The microneutralization test (MNT) and type-2-specific solid-phase radioimmunoassay (SPRIA) were used as serological tests. No difference in the prevalence of HSV-2 antibody between the patients and controls was revealed by either test. Various combinations of the results from the two tests also failed to show any difference between patients and controls. Moreover, no significant differences were observed in the prevalence of HSV-2 antibody between patients suffering from the various pathological conditions and those diagnosed at enrollment and later in the course of the study. These results do not provide any support for the hypothesis of the involvement of HSV-2 in cervical neoplasia.

High reproduction capacity of recombinants between H3N2 human influenza and fowl plague viruses is due to the gene coding for M proteins.

Recombinants between H3N2 human influenza viruses (A/Victoria/3/75 and A/Bangkok/1/79, low-yielding parents in chick embryos) and fowl plague virus (FPV, a high-yielding parent in chick embryos) have been obtained. The high reproductive capacity of recombinants in chick embryos has been shown to be due to the gene coding for M proteins.

Some properties of RNA polymerases of different influenza viruses.

The transcriptases of several influenza viruses were tested for pH and temperature dependence and for thermal stability. Marked differences in pH dependence and thermostability were determined.