Genome screen for asthma and related phenotypes in the French EGEA study.

A genome-wide search was conducted in 107 nuclear families with at least two siblings with asthma, as part of the French EGEA study. A two-stage analysis strategy was applied to the 107 families divided into two independent subsets of 46 and 61 families, where all regions detected in the first set of families were tested for replication in the second set. In addition, all regions reported by published genome scans in different populations were examined in the total sample. A total of 254 markers were typed in the first set of families and 70% of them in the second set. Linkage was investigated by model-free methods for asthma and four asthma-related phenotypes: bronchial responsiveness (BR), skin test response, total immunoglobulin E (IgE) levels, and eosinophil count. The two-stage analysis led to the detection of three regions: 11p13 for IgE, 12q24 for eosinophils, and 17q12-21 for asthma and skin tests. Among the regions reported by published genome screens, seven were found in the 107 French EGEA families: three being already detected by the two-stage analysis, 11p13 (p = 0.005), 12q24 (p = 0.0008), and 17q12-21 (p = 0.001), and four additional ones, 1p31 (p = 0.005) for asthma, 11q13 (p = 0.006) for IgE, 13q31 (p = 0.001) for eosinophils, and 19q13 (p = 0.02) for BR.

Effect of interferon alpha on high serum androgen concentrations in HIV positive men with Kaposi's sarcoma.

AIM: To measure serum androgen concentrations in men with HIV related Kaposi's sarcoma (KS) who had been treated with recombinant interferon (IFN) alpha-2a to determine the role of androgens on the development of KS lesions. METHODS: 32 men with HIV related KS who had been treated with IFN were studied: 24 men in complete KS remission and eight not in remission. Serum androgen concentrations were determined before, during, and after IFN treatment and correlated with clinical remission. RESULTS: All patients in complete KS remission had lower serum androgen concentrations following IFN treatment: -51% for dehydroepiandrosterone (DHEA) (p < 0.0001); -38% for DHEA sulphate (p < 0.002);-39% for androstenedione (p < 0.002); and -44% for testosterone (p < 0.007). These decreases brought the serum concentrations to about normal levels. However, IFN had varying effects on serum androgen concentrations in the men not in remission: a small decrease, a large increase in one androgen, or no change in serum androgens. CONCLUSIONS: The association between serum androgen levels and the progression or remission of HIV associated KS suggests that androgens affect the development of KS lesions. A clear understanding of the changes in the androgen environment may provide a sound basis for the development of new therapeutic strategies.

Hypothalamo-pituitary-adrenal function in human immunodeficiency virus-infected men.

We prospectively studied adrenal function in 51 human immunodeficiency virus-positive male patients, including heterosexuals, homosexuals, and iv drug users, classified according to 1987 CDC criteria as belonging to stages II/III or IVC. Basal serum concentrations of cortisol (F), progesterone (P4) and 17 alpha-hydroxyprogesterone (17 alpha-OHP4) were determined during the two stages. In stage IVC patients, the circadian rhythms of ACTH and F were assessed, and ovine CRH (oCRH) and immediate cosyntropin-stimulating tests were evaluated. Serum concentrations of hormones were analyzed in relationship to the absolute CD4 cell count in all subjects. The mean serum F concentration in stage IVC patients, the mean P4 concentration in stage II/III and IVC patients, and the mean 17 alpha-OHP4 level in stage II/III patients were significantly increased compared to control values (P < 0.0001, P < 0.0001, and P < 0.002, respectively). The mean serum F concentration in stage IVC patients was significantly increased compared to that in stage II/III patients (P < 0.004), and the mean serum 17 alpha-OHP4 concentration in stage II/III patients was significantly increased compared to that in stage IVC patients (P < 0.02). In the 22 stage IVC patients, the circadian rhythms of ACTH and F were normal in all but 7 for ACTH and 5 for F, whereas oCRH test results indicated that 14 of them had reduced or blunted responses. By contrast, cosyntropin stimulation results were normal. CD4 cell counts were significantly negatively correlated with the serum F concentration (P < 0.02). In conclusion, during human immunodeficiency virus infection, the serum F concentration was negatively correlated with CD4 cell counts. Cosyntropin test results were normal, but 63% of the stage IVC men had abnormal responses to oCRH.

Relationship between sex steroid hormone levels and CD4 lymphocytes in HIV infected men.

The serum concentrations of the steroid, androgens and estrogens, in the HIV-positive male patients were studied. These men belonged to one of the three main behaviour groups: heterosexual (He), drug addicts (DA) and homosexual (Ho) at early stages (II and III) or at advanced stage of AIDS (IVC), classified according to the Centers for Disease Control (CDC). The circulating concentrations of sex steroids were then analysed with reference to the risk factors, absolute CD4 cell count and the progression of HIV infection. Regardless of risk factors, the stage II and III HIV-infected patients had serum dehydro-epiandrosterone sulfate (DHEAs) (+37%, p < 0.03), testosterone (T) (+24%, p < 0.006) and estrone (E1) (+170%, p < 0.0001) levels higher than those of controls. The patients IVC stage had low serum DHEAs (-48%, p < 0.0001) and elevated estradiol (E2) (+200%, p < 0.0001). According to risk factors, there were no significant differences in androgen and estrogen concentrations between the behaviour groups. There were significant positive correlations between the CD4 cell count and the serum concentrations of DHEAs (p < 0.0001), DHEA (p < 0.01) and E1 (p < 0.006). This suggests that there is a relationship between the circulating sex hormone levels, particularly DHEAs, and the progression of immune depression in HIV, whatever the risk factor. The observed association between DHEAs and the progression of HIV infection suggests that this androgen may play a role in the normal function of the immune system.

Postprandial free fatty acids stimulate activity of human corticosteroid binding globulin.

The effect of postprandial variation of free fatty acids (FFA) on serum corticosteroid binding globulin (CBG) properties and cortisol (hydrocortisone) concentrations were explored in 11 women (20-30 yr) during 8 h after an oral load of tallow (26% C16:0, 18% C18:0, and 43% C18:1), oleic-sunflower (oleic-SF; 73% C18:1), sunflower (SF; 67% C18:2), and mixed oil (MO; 39% C18:1 and 48% C18:2). Serum FFA increased little after SF and MO but more than doubled in the late postprandial period (6 and 8 h) after oleic-SF (due to monounsaturated FFA) or tallow (due to saturated and monounsaturated FFA). CBG concentrations remained unchanged, but in relation with the postprandial elevation of serum FFA, CBG binding activity was increased after tallow or oleic-SF as a result of a combined two- to threefold increase in affinity constant and a 50% reduction in binding sites. Immunological and in vitro binding studies showed the changes in CBG behavior to be conformational and to be mediated mainly by monounsaturated FFA, especially C18:1. The modifications of CBG properties were associated with sustained high concentrations of cortisol (suppression of midday decrease) 6 and 8 h after tallow or oleic-SF. Thus dietary FFA may have an impact on bioavailability of glucocorticoids.

Differences in androgens of HIV positive patients with and without Kaposi sarcoma.

AIM: Since most forms of Kaposi sarcoma are much more common in men than in women, the aim of this study was to examine serum concentrations of sex steroids in HIV positive men with and without Kaposi sarcoma. METHODS: Blood samples from 34 HIV positive men without Kaposi sarcoma (KS-) and 28 with Kaposi sarcoma (KS+) and from 35 HIV negative men (controls) were analysed for adrenal and gonadal steroids. Further analysis was done in subgroups classified by CD4 lymphocyte counts. RESULTS: KS+ patients had significantly higher serum dehydroepiandrosterone (DHEA) and testosterone concentrations than the KS- patients, and their DHEA, DHEA sulphate, testosterone, and androstenedione values were higher than in the controls. The KS+ patients with more than 500 CD4 lymphocytes per mm3 had significantly higher serum DHEA, DHEA sulphate, and testosterone than the KS- patients with the same CD4 counts; those with 500-200 CD4 cells/mm3 had higher serum DHEA and testosterone than the equivalent KS- men; and those with < 200 CD4 cells/mm3 had raised DHEA only compared with KS- men. Both KS+ and KS- men had higher serum progesterone and oestradiol than the controls. Glucocorticoids were not significantly altered. CONCLUSIONS: The high androgen levels in KS+ patients, particularly in the early stages of the disease (> 500 CD4 cells/mm3), may affect the immune system by inducing an abnormal cytokine profile, or by increasing T8 proliferation and activation, or both. This raises the question of the relationship between androgens and Kaposi sarcoma.

Unsaturated fatty acids synergistically enhance glucocorticoid-induced gene expression.

Regulation by unsaturated fatty acids of glucocorticoid-sensitive gene transcription was studied in HeLa cells transiently transfected with a mouse mammary tumour virus-luciferase reporter gene. Arachidonic acid and docosahexaenoic acid by themselves had no effect on basal levels of luciferase expression. However, they were able to enhance dexamethasone-induced transcription by 1.4-2.3 times (25-42 times the control levels) in a dose-dependent manner (ED50: 18 and 8 microM) for arachidonic and docosahexaenoic acid, respectively. The glucocorticoid antagonist RU486 effectively antagonized the dexamethasone response as well as the synergistic effect observed in the presence of arachidonic and docosahexaenoic acids, suggesting that the glucocorticoid receptor was an intermediate in the fatty acid synergism of the dexamethasone response. These studies show that fatty acids may be playing a role in modulating the intracellular steroid hormone signalling pathway to co-regulate a glucocorticoid-sensitive promoter.

Serum lipid concentration with reference to the clinical and immunological status of HIV infected men.

We investigated the serum concentrations of free fatty acids (FFA), cholesterol, phopholipids and triglycerides in HIV-positive men (n = 50) from three behaviour groups: heterosexuals (n = 16), drug addicts (n = 18) and homosexuals (n = 16) and a control group of HIV-negative men (n = 25). The circulating concentrations of lipids were analyzed with reference to the clinical status of infection and the absolute CD4 cell count. According to the clinical progression of HIV infection the patients were divided into two groups (CDC 1987 criteria): stages II and III (n = 28) and stage IVC (n = 22). HIV-positive men had higher polyunsaturated fatty acids (PUFA) (+100%), p < 0.001) only in the II and III stages, lower cholesterol (-25% to -40%, p < 0.001) and lower phospholipids (-25%, p < 0.001) for the two stages than in the controls. The triglycerides were increased only in stage IVC patients compared to the controls (+110%, p < 0.001). According to their CD4 cell count, the patients were divided into four groups: > 400 (n = 11), 400-150 (n = 9), 150-50 (n = 9) and < 50 (n = 19). Regardless of the CD4 count, the PUFA were significantly higher (+50% to +125%) and cholesterol (-35% to -45%) and phospholipids (-25% to -30%) lower than in the controls in all HIV-infected men except the patients with 400-150 CD4. Only the HIV-positive patients with < 50 CD4 cells had elevated triglycerides (+97%, p < 0.001). There was a significant negative correlation between the CD4 cell count and the serum triglyceride concentrations (r = -0.31, p < 0.03). In conclusion, the most elevated PUFA occurred in HIV-positive patients with > 400 CD4, while hypertriglyceridaemia is prevalent in very advanced stages of infection (with < 50 CD4). This suggests that there is a relationship between the circulating PUFA and triglycride levels and the progression of infection and immune suppression. The disturbances in lipid metabolism must now be correlated with the underlying metabolic, hormonal and cytokine changes and their role in the development of significant malnutrition and immune perturbations.

Effect of estradiol on endotoxin-induced changes in steroid hormone levels and lethality in male rats.

We examined the effect of exogenous estradiol on the changes in serum steroid hormone levels induced by a nonlethal dose of Escherichia coli endotoxin in male rats and the deaths due to nonlethal and lethal doses of endotoxin. Injection of estradiol 5 min before a nonlethal dose of endotoxin changed the serum sex steroid hormone response of male rats to endotoxin. The serum estrogen concentrations of estradiol + endotoxin-treated rats decreased by 50% (P < 0.001), while those of the endotoxin-treated rats increased (2- to 5-fold). The serum androgen concentrations of estradiol + endotoxin-treated rats did not change significantly, while those of endotoxin-treated rats dropped to 30-40%, P < 0.001. Exogenous estradiol also appeared to influence the percentage of endotoxin-induced deaths in a dose-dependent manner. It reduced the number of deaths induced by nonlethal (2 mg/kg) dose of endotoxin but increased the number of deaths induced by a highly lethal dose (8 mg/kg). These results, together with the known relationships between estrogen and the immune response, suggest that estrogens affect the course of septic shock in a complex fashion and may have either protective or deleterious effect.

Free fatty acid profiles in the non-obese diabetic (NOD) mouse: basal serum levels and effects of endocrine manipulation.

The non-obese diabetic mouse (NOD) is one of the few available models of spontaneous autoimmune insulin-dependent diabetes mellitus (IDDM). The authors determined the free fatty acid (FFA) levels and the concentrations and relative percentages of the various classes of FFA before the onset of diabetes in both sexes at 2 and 4 months of age and in diabetic females. A circadian rhythm of FFA concentrations was found in prediabetic mice, with lower values in the evening. Moreover, there was a sex difference in FFA concentrations in the morning, with 2-month-old females having higher concentrations than males. Sex and age-related differences were also observed in the concentrations of the various classes of FFA, with higher polyunsaturated fatty acid concentrations in 2-month-old females and increases in di- and tri-unsaturated fatty acids concentrations in both sexes with age. Hormonal manipulation such as adrenalectomy and/or castration modulated total FFA and the concentrations of the various classes of FFA in 2-month-old mice. These FFA differences between males and females should be taken into account in the onset of type I diabetes.

Perturbation of the immunosuppressive action of glucocorticoids in rat thymocytes by liposoluble extracts of serum from AIDS patients.

Liposoluble extracts of serum from healthy men and AIDS patients (stages IVC1 and IVD by CDC criteria) inhibited the incorporation of [3H]thymidine into isolated rat thymocytes, but AIDS extracts were less inhibitory, requiring 1.8 times more cortisol in the AIDS extracts than in the healthy extracts to inhibit [3H]thymidine incorporation by 50%. Although the total serum extracts from AIDS patients contained 1.7 times more cortisol than the extracts from healthy controls, the AIDS extracts decreased the binding affinity (Ka) of [3H]dexamethasone to rat thymus glucocorticoid receptors by 50% less than the healthy control extracts. The present study seems to indicate that a substance(s) can be extracted from the serum of AIDS patients that attenuates the inhibitory effect of cortisol on thymocyte proliferation and interferes with the binding of cortisol to the glucocorticoid receptor.

Stimulation of the binding properties of adult rat corticosteroid-binding globulin by a lipolysis-induced rise in plasma free fatty acids.

In vitro studies have shown that FFA induce conformational changes in human corticosteroid-binding globulin (CBG). We increased the plasma FFA concentrations of adult male rats by injecting heparin to determine whether such changes in CBG binding and immunological properties also occur in vivo. The in vivo transient activation of lipase by heparin produced a large increase in plasma FFA at 10 and 20 min (P < 0.01), which was maximal at 60 min (P < 0.005) and remained elevated at 120 min (P < 0.01) postinjection. This rise in FFA was associated with a 2- to 3-fold increase in the binding indices (C values; liters per g) of corticosterone (B) and progesterone to CBG 60-120 min postinjection (P < 0.001). There was a good positive correlation (r = 0.85) between the increase in B binding and the rise in plasma FFA in heparin-treated rats. The enhanced B binding to CBG resulted from a 2-fold increase in the apparent number of binding sites, without any significant change in the affinity constant (Ka). FFA extracted from postheparin plasma and a standard FFA mixture induced similar changes in B binding to purified mature rat CBG. The immunological behavior of CBG was not significantly changed after heparin-induced lipolysis, but the immunoreactivity of CBG from heparin-treated rats was more reduced by incubation with exogenous FFA than that from controls. FFA extracted from the plasma of heparin-treated rats and a standard FFA mixture both produced a dose-dependent drop in the immunodetection of pure CBG. These binding and immunological studies indicate that FFA mediate conformational changes in rat CBG in vivo. Thus, FFA, in addition to their roles as metabolic energy sources and components of complex lipids, can be rapid potent endogenous modulators of steroid-protein interactions.

Modulation of glucocorticoid binding to rat liver cytosol receptor by lipid-soluble extracts from the serum of AIDS patients.

The total liposoluble extract of sera from AIDS patients, IVC1 and IVD stages, containing cortisol and free fatty acids (FFA) inhibited [3H]dexamethasone binding to a lesser extent than did the same quantity of total liposoluble extract of sera from healthy men. FFA isolated from extracts of AIDS sera by Sephadex LH20 chromatography had less effect on [3H]dexamethasone binding to rat liver glucocorticoid receptor than those extracted from sera of healthy men. These results suggest the presence in sera of AIDS patients of a liposoluble substance which could be limiting the inhibitory effect of FFA on [3H]dexamethasone binding to glucocorticoid receptor by inducing a conformational change in glucocorticoid receptor that could alter the biological action of glucocorticoids. The pathological consequence could be the apparent contradiction of high cortisolemia and clinical symptoms of adrenal insufficiency that have been observed in AIDS patients.

In vivo transient rise in plasma free fatty acids alters the functional properties of alpha-fetoprotein.

Previous in vitro studies have shown that unsaturated fatty acids (UFA) induce conformational changes in rodent and human alpha-fetoprotein (AFP). To determine whether such changes in the binding and immunological properties of rat AFP also occur in vivo, plasma free fatty acid (FFA) concentrations were increased in young male rats (15, 21 and 28 days old) by acute i.v. injection of heparin (200 IU/kg). Plasma estrogens (estrone and estradiol) did not change after injection of heparin. There was a large increase in plasma FFA 10-20 min post-heparin injection, with a return to normal 60 min later. This transient rise in FFA plasma was associated with a 50% drop (P less than 0.001) in the binding of estradiol to rat AFP of 15-, 21- and 28-day-old rats by reducing the number of binding sites (P less than 0.001), leaving the affinity constant (Ka) unchanged. FFA extracts from post-heparin plasma induced similar changes in estradiol binding to purified rat AFP. The rise in plasma FFA induced a loss of AFP immunoreactivity, in 21- (P less than 0.001) and 28-day-old rats (P less than 0.001), but not in 15-day-old rats. This age-dependent response correlated with the FFA/AFP molar ratio (38 in 15-day-old rats, 388 in 21-day-old rats, and 5600 in 28-day-old rats). These results indicate that an in vivo rise in FFA induces rapid and reversible conformational changes in AFP which may modulate the endocrine and immune function of this oncofetal protein.

Effect of the aromatase inhibitor, 4 hydroxyandrostenedione, on the endotoxin-induced changes in steroid hormones in male rats.

The increase in circulating estrogen concentrations that follows injection of Escherichia coli endotoxin (Endo) may be due to increased aromatase activity. We have therefore analysed the effect of the aromatase inhibitor, 4 hydroxyandrostenedione (4OHA) on the steroid hormone response of male rats, particularly the dramatic increase in estrogens and decrease in androgens, induced by Endo. The concentrations of corticosterone (B), progesterone (P4), 17 alpha hydroxyprogesterone (17 alpha OHP4), androstenedione (delta 4), testosterone (T), estrone (E1) and estradiol (E2) were determined 2 hours after injection of increasing doses of 4OHA with and without Endo. The increase in serum estrogen concentrations and drop in serum androgen levels in response to Endo were blocked by a single dose of 4OHA. The effect of 4OHA appeared to be dose dependent. Low doses (30 mg/kg and 50 mg/kg) induced significant changes in the estrogen and androgen responses, but the high dose (100 mg/kg) blocked all changes in sex steroids induced by Endo. 4OHA did not alter the Endo-induced changes in other steroids.

Evidence for changes in adrenal and testicular steroids during HIV infection.

The serum levels of cortisol, progesterone, 17 alpha-hydroxyprogesterone, dehydroepiandrosterone (DHEA), DHEA sulfate, androstenedione (delta 4), testosterone (T), estrone, and estradiol of HIV+ men and HIV- men were determined by radioimmunoassay. The cortisol, 17 alpha-hydroxyprogesterone, and estrone levels of all HIV+ subjects were 35-55% (p less than 0.01), 25-90% (p less than 0.01), and 30-50% (p less than 0.01) higher, respectively, than those of controls. Androgen levels were very high in Centers for Disease Control (CDC) groups II and III of HIV infection (DHEA, 85%, p less than 0.01; delta 4, 60%, p less than 0.01; T, 30%, p less than 0.05), but much lower in group IVC1 and IVC2. The estradiol levels were significantly elevated only in group IVD (50%, p less than 0.01) and group IVC2 (25%, NS). These results indicate that serum hormone levels are correlated with HIV infection group. The changes in steroid hormone concentrations during the development of HIV infection may have important implications for the immune response of patients. The high cortisol and estrone levels of all groups, the elevated androgen levels in asymptomatic groups, and the low androgens in AIDS patients may form part of the complex network of immunomodulatory factors.

Endotoxin induced changes in serum estrogen in male rats: influence of testicular maturation.

The influence of acute endotoxin (Endo) administration on adrenal and testicular serum hormones, corticosterone (B), progesterone (P4), 17 alpha OH progesterone (17 alpha OH P4), androstenedione (delta 4), testosterone (T), estrone (E1) and estradiol (E2) was studied in male rats aged 8, 12 and 15 weeks. The present study confirms that the concentrations of circulating steroid hormones in male rats vary with age, and indicate that the adrenal glands mature before the testes. The steroid response to Endo is age-dependent. B, P4, 17 alpha OH P4 was increased and T decreased in all animals. But, there was a very significant increase in estrogens (E1 and E2) and a decrease in delta 4 only in male rats aged 12 weeks and over. The lack of an estrogen response to Endo injection in 8 week-old rats may indicate that the reduced sensitivity (refractory period) to Endo (which has been reported to last until 21 days of age) continues longer. The reduced sensitivity to Endo which occurs in young rats could be due in part to the absence of adrenal-testicular cooperation as a result of partial testicular immaturity.

A simple computer programme for standard curve tracing and calculations in RIA following sigmoid patterns.

A computer programme is described for the analysis of radioimmunoassays assuming a general sigmoid shape. The mathematical treatment uses the results obtained from a sigmoid equation to perform a limited operational search in order to optimize the fitness of the curve. The programme can be installed in most desk top microcomputers and has been tested for the calculation of Ig concentrations in biological fluids.

Activation of the human classical complement pathway by a mouse monoclonal hybrid IgG1-2a monovalent anti-TNP antibody bound to TNP-conjugated cells.

A mouse hybridoma selected and cloned for anti-TNP specificity produced three distinct monoclonal antibody species that were separated on protein A-Sepharose by stepwise acid elution. The IgG1 kappa product of the parental myeloma was eluted at pH 6.0. An IgG2a kappa bivalent anti-TNP antibody was eluted at pH 4.5, whereas elution at pH 5.0 yielded a hybrid IgG1-2a kappa monovalent anti-TNP antibody. The IgG2a molecules agglutinated TNP-conjugated sheep erythrocytes (TNP-ES) and lysed TNP-ES in the presence of normal human serum (NHS). Hybrid IgG1-2a antibody was also capable of lysing the cells in NHS, although it did not agglutinate TNP-ES. A threshold in monovalent antibody input was necessary for the lysis of TNP-ES, indicating a requirement for a minimal density of bound monovalent IgG to trigger complement activation. Lysis occurred in NHS-VBS++ but not in NHS-MgEGTA, and it was associated with a dose-dependent consumption of C1, C4, and C2 hemolytic activities. Quantitation of the antibody bound to TNP-ES when using radiolabeled rabbit anti-mouse Fab antibody demonstrated that for similar inputs, 5.4 times as much bivalent as monovalent antibody bound to TNP-ES. When similar amounts of antibody were effectively bound to TNP-ES, monovalent hybrid IgG1-2a was five times less efficient than bivalent IgG2a to yield 50% cell lysis in the presence of NHS. These results indicate that neither bivalent binding nor the presence of two identical heavy chains are necessary requirements for antibody-dependent activation of the classical complement pathway.

Enhancement of Lewis lung carcinoma growth by sera or spleen cells from tumour-bearing mice.

Lewis lung carcinoma(3LL) cells grafted in syngeneic adult C57BL/6 mice produced local tumours associated with lung metastasis in 78% of recipients. Adult thymectomized, lethally irradiated, bone marrow cell-reconstituted animals (B mice) were more resistant since this tumour grew in only 46% of recipients and especially the weight of lung metastasis was almost 8 times less than in normal animals. Sera from tumour-bearing mice transferred into B mice enhanced tumour incidence and weight of metastasis to the level observed in normal mice. In vitro cultured 3LL cells displayed an intense mitogenic activity as measured by 3H-thymidine incorporation. Addition into these cultures of serum from tumour-bearing animals did not alter this activity. Addition of normal spleen cells in a ratio 40/1 reduced this mitogenic activity to a half or a third. Spleen cells from tumour-bearing mice, either normal or serum-enhanced B mice, mixed in vitro with 3LL cells, produced a 4-fold increase of mitogenic activity of the latter. These results indicate that the lymphoid system may contribute to the growth and spreading of 3LL tumours.