Salt bridge impact on global rigidity and thermostability in thermophilic citrate synthase.

It has been suggested that structural rigidity is connected to thermostability, e.g. in enzymes from thermophilic microorganisms. We examine the importance of correctly handling salt bridges, and interactions which we term 'strong polars', when constructing the constraint network for global rigidity analysis in these systems. Through a comparison of rigidity in citrate synthases, we clarify the relationship between rigidity and thermostability. In particular, with our corrected handling of strong polar interactions, the difference in rigidity between mesophilic and thermophilic structures is detected more clearly than in previous studies. The increase in rigidity did not detract from the functional flexibility of the active site in all systems once their respective temperature range had been reached. We then examine the distribution of salt bridges in thermophiles that were previously unaccounted for in flexibility studies. We show that in hyperthermophiles these have stabilising roles in the active site; occuring in close proximity to key residues involved in catalysis and binding of the protein.

Helicobacter pylori: an emerging infectious disease.

Helicobacter pylori is the most common chronic bacterial infection in the world, colonizing the stomachs of more than 50% of the human population. The discovery of this bacterium has changed the concept of care and management for peptic ulcer disease, mucosa-associated lymphomas, gastritis, and gastric carcinoma. Although the mode of transmission is not definitively known, person-to-person contact is suspected. This article discusses H. pylori, the associated clinical syndromes and diseases, risk factors, and current pharmacologic management.

A model of Na-K-2Cl cotransport based on ordered ion binding and glide symmetry.

In the duck red blood cell, Na-K-2Cl cotransport exhibits two modes of ion movement: net cotransport and obligate cation exchange. In high-K cells, the predominant exchange is K/K (or K/Rb). In high-Na cells, it becomes Na/Na (or Na/Li). Both represent partial reactions in which a fully loaded carrier releases part of its cargo, rebinds fresh ions, and returns back across the membrane fully loaded. Net cotransport occurs when the carrier unloads completely and returns empty. This mode has a fixed stoichiometry of 1Na:1K:2Cl under all conditions tested. The ion requirements of the two exchanges differ: K/K exchange requires only K and Cl outside but all three ions inside. Na/Na exchange requires all three ions outside but only Na inside. We propose a simple model in which the carrier can only move when either fully loaded or completely empty and in which the ions bind in a strictly ordered sequence. For example, externally, a Na binds first and then a Cl, followed by a K and a second Cl. Internally, the first on is the first off (glide symmetry), so the Na is released first and then the first Cl, followed by the K and finally by the second Cl. Only then can the empty form return to the outside to start a new cycle.

Abnormalities of CD45 isoform expression in HIV infection.

Using monoclonal antibodies against CD45, CD45RA, CD45RB, and CD45RO, the surface density of expression and proportions of different CD45 isoforms were analyzed on CD4+ and CD8+ T lymphocyte subsets in HIV+ patients and controls. Analysis of the relative specific fluorescence (RSF) of CD45 isoforms showed a significant reduction in expression of total CD45 and its isoforms, CD45RA, CD45RO, and CD45RB, on CD4+ and CD8+ lymphocyte subsets in HIV+ patients compared with controls. However, expression of phosphotyrosine in the cytoplasm of CD4+ and CD8+ lymphocytes did not differ significantly between HIV+ patients and controls. Percentages of "naive" CD45RA+RO- CD4+ and CD8+ lymphocytes were lower than control values in all HIV+ patients (P < 0.001). Compared with controls, HIV+ patients had similar percentages of "memory" CD45RA-RO+ CD4+ lymphocytes but significantly higher percentages of memory CD8+ lymphocytes (P < 0.001). Percentages of memory CD8+ lymphocytes were lowest in patients with AIDS (P < 0.001). The consistent reduction in surface expression of all CD45 isoforms observed in our study may be of relevance to the impaired T cell activation characteristic of HIV infection. Also, our results argue against the selective depletion of memory CD4+ lymphocytes in HIV-induced disease.

Cell cycling in HIV infection: analysis of in vivo activated lymphocytes.

Infection with HIV results in increased circulating levels of T lymphocytes expressing phenotypic markers of immune activation. In the present study, using three-colour immunofluorescence, we examined the cell cycle status of these activated cells. Activated (HLA-DR+, CD25+ and CD38+) CD4+ and CD8+ T lymphocytes in peripheral blood were analysed for DNA content in 15 HIV+ patients and 10 healthy age- and sex-matched control subjects. As expected, all HIV+ patients had elevated percentage levels of activated CD4+ HLA-DR+, CD4+ CD25+, CD8+ HLA-DR+, CD8+ CD25+ and CD8+ CD38+ T lymphocytes compared with control subjects (P < 0.001 for all). Percentage levels of CD4+ HLA-DR+ and CD8+ HLA-DR+T lymphocytes in the 'proliferative' (S-G2M) phase of the cell cycle were also higher in the HIV+ patients compared with controls (P < 0.001 for both). The percentage levels of proliferative CD4+ CD25+, CD8+ CD25+ and CD8+ CD38+ lymphocytes were, however, similar in HIV+ patients and controls, indicating that the proliferative fraction of cells in vivo was confined to the HLA-DR+ subset and absent from the CD25+ and CD38+ populations. Four HIV+ patients had grossly elevated levels of CD8+ lymphocytes which were CD38+ (> 95%) and confined to the pre-G0-G1 phase of the cell cycle, suggesting these may be cells committed to apoptosis. These observations indicate an increase in the proliferative capacity of HLA-DR+ T lymphocytes in HIV infection in vivo. The reduced DNA content in other populations (e.g. CD38+ CD8+ lymphocytes) of some patients with advanced HIV disease suggests that these cells are apoptotic. Thus our results define both proliferative and apoptotic processes as a spectrum of activation-related events in HIV infection.

Energy expenditure and wasting in human immunodeficiency virus infection.

BACKGROUND: Increased expenditure of energy at rest has been considered a contributing factor to the negative energy balance and weight loss that occur in patients with human immunodeficiency virus (HIV) infection. However, the true determinant of energy balance is not resting but total energy expenditure. We sought to determine the contribution of total energy expenditure to weight changes in patients with HIV-associated wasting. METHODS: We performed 51 assessments of energy metabolism in 27 men with HIV infection at different stages of disease, including periods of both rapid and slow weight loss. Resting energy expenditure was measured by indirect calorimetry, total energy expenditure by the doubly-labeled-water technique, and energy intake by recording the weight of food consumed. The results were compared with the rate of weight loss or gain. RESULTS: The mean (+/- SD) total energy expended by the HIV-infected men was 2750 +/- 670 kcal per day, no more than that expended by normal men. There was a significant positive relation between total energy expenditure and the rate of weight change (r = 0.61, P < 0.001); thus, during rapid weight loss, total energy expenditure was reduced to 2180 +/- 580 kcal per day (P = 0.009), primarily because of reduced physical activity. During rapid weight loss, the negative energy balance (-850 +/- 580 kcal per day) was primarily the result of the reduction in energy intake, to 1330 +/- 610 kcal per day; intake correlated strongly with the rate of weight change (r = 0.84, P < 0.001). CONCLUSIONS: In patients with HIV infection, total energy expenditure is reduced during episodes of weight loss. Reduced energy intake, not elevated energy expenditure, is the prime determinant of weight loss in HIV-associated wasting.

Schistosomiasis as a cause of chronic lower abdominal pain.

BACKGROUND: Chronic intestinal schistosomiasis is rare in the United Kingdom. The symptoms are nonspecific and may mimic several other gastrointestinal conditions. We present a case of chronic intestinal schistosomiasis in a West Indian woman presenting to a genitourinary clinic. CASE: The patient presented with chronic lower abdominal pain and dysuria. A sexually transmitted disease (STD) screen was negative and midstream urine cultures were sterile. A rectal biopsy revealed a non-necrotizing granulomatous reaction around the ova of Schistosoma. Her symptoms resolved with anti-schistosomiasis therapy. CONCLUSION: This case illustrates that physicians should be aware of chronic schistosomiasis in the differential diagnosis of chronic lower abdominal pain in women who have come from or visited areas where schistosomiasis is endemic.

Markers of immune cell activation and disease progression. Cell activation in HIV disease.

Immune cell activation is a feature of infection with the human immunodeficiency virus (HIV). Here we report our studies on a cohort of over 400 patients with HIV infection studied cross-sectionally and longitudinally to examine the relationship between markers of immune cell activation and disease progression. To examine disease progression, 340 patients with HIV infection but without AIDS were followed for a total of 574 patient years, during which 56 developed AIDS. In our first study, 157 patients in CDC groups II-IV were examined cross-sectionally for in vivo expression of the activation markers HLA-DR and CD25 on CD3, CD4 and CD8 T cells. Levels of CD3+ HLA-DR+ T cells are high in HIV infection and show a significant negative correlation with CD4 counts (r = 0.52; p < 0.001). The appearance of HLA-DR+ CD3+ T cells is an early feature of asymptomatic HIV+ patients, with a greater proportion (82%) showing abnormally high levels of these than abnormally low levels of CD4 (52%; p < 0.001). Examining activation of the CD4 subset specifically is likely to be of greater interest, given that this cell is the viral target. Indeed, we found that in the cross-sectional study, levels of HLA-DR+ and CD25+ CD4 lymphocytes show a step-wise linear increase with increasing disease severity (significant test for linear trend; p < 0.001). In our previous studies, only declining CD4 count has shown such a significant linear trend. These data suggest that measuring activated CD4+ T cells in the periphery may be a powerful predictive tool. In our second study, we examined the expression of other markers acquired (CD45R0) and lost (CD45RA) following activation of naïve T cells. Examining expression of these on CD4 and CD8 cells cross-sectionally in 71 HIV+ patients, we found abnormalities in percentage levels of CD45RA+ and CD45R0+ populations, none of which showed any relationship to disease severity. Intriguingly, however, we noted that the surface density of both CD45RA and CD45R0 molecules on CD4 and CD8 cells was markedly and significantly reduced at all stages of HIV infection (eg relative specific fluorescence reduced by up to 50%; p < 0.001). This abnormality was confirmed in studies using antibodies to a common epitope on all CD45 isoforms (pan-CD45) and to the CD45RB isoform. Finally, returning to the question of immune cell markers of activation and disease progression, we have examined some of the best documented markers in our longitudinal study.(ABSTRACT TRUNCATED AT 400 WORDS)

Gay men as victims of nonconsensual sex.

Incidents of nonconsensual sexual activity among 930 homosexually active men living in England and Wales are analyzed. Of these men, 27.6% said they had been sexually assaulted or had sex against their will at some point in their lives; one third had been forced into sexual activity (usually anal intercourse) by men with whom they had previously had, or were currently having, consensual sexual activity. The contention that male rape is usually committed by heterosexually identified men, primarily as an expression of power and control, is not supported. Recognition that gay men rape other gay men is needed, both by the gay community and support services for victims.

Alcohol, AIDS and immunity.

In order to understand the potential impact of alcohol consumption on the course of the HIV/AIDS pandemic we examine at least 3 very different debates. In an attempt to summarise these debates we assess the impact of alcohol consumption on numerous aspects of HIV infection, including the relationship between alcohol use and likelihood of engagement in 'unsafe' sexual behaviour; the impact of alcohol on immune function and its importance as a co-factor for AIDS-related illness. We argue that, contrary to popular belief, the consumption of alcohol does not appear to make individuals more likely to engage in unsafe sex. Furthermore, while alcohol has clearly been proven to effect immune function in vivo and in vitro there is no clear evidence that it plays any part in individuals' susceptibility to HIV infection or has any effect on disease progression among persons with HIV infection. Clearly some of this research is in its infancy and such conclusions should be treated with caution.

T cell activation and disease severity in HIV infection.

In vitro studies have indicated that T lymphocyte activation may be of importance in the pathogenesis of HIV infection. In order to define the role of immune activation in vivo, we assessed the expression of the T cell activation markers HLA-DR and CD25 by flow cytometry in peripheral blood in relation to disease severity and the surrogate markers CD4 and beta 2-microglobulin in 157 patients with HIV infection and 53 healthy seronegative blood donors. Percentage levels of CD3+HLA-DR+ T lymphocytes were significantly higher (P < 0.0001) and percentage levels of CD3+CD25+ T lymphocytes significantly lower (P < 0.0001) in all HIV+ patients compared with controls. A significant correlation was observed between increasing percentage levels of CD3+HLA-DR+ T lymphocytes and both declining CD4 counts (r = 0.52; P < 0.001) and increasing beta 2-microglobulin levels (r = 0.56; P < 0.001). Percentage levels of CD4+HLA-DR+ and CD4+ CD25+ lymphocytes were significantly higher in all HIV+ patients compared with controls (P < 0.001). Levels of activated (HLA-DR+ and CD25+) CD4+ lymphocytes showed a significant step-wise linear increase with increasing disease severity (P < 0.001). High levels of CD3+HLA-DR+ T lymphocytes were found in a greater proportion (81.8%) of asymptomatic HIV+ patients (Centres for Disease Control (CDC) group II) than low CD4 counts (51.5%) (P < 0.001). Compared with controls, HIV+ patients had higher percentage levels of CD8+HLA-DR+ lymphocytes (P < 0.001), but similar levels of CD8+CD25+ lymphocytes. These results indicate that T cell activation is not only a consistent but also an early feature in HIV infection. Monitoring levels of activated T cells and their subsets is of value in assessing progression of HIV-related disease.

Sex role separation in sexual diaries of homosexual men.

OBJECTIVE: To measure types of sex role prevalence in common and risk-related behaviours among gay men for modelling HIV transmission. DESIGN: Cohort study of 385 homosexually active men recording sexual diaries over 1-month periods. METHODS: Measures of incidence of behavioural sex roles for masturbation, fellatio, anal intercourse and anilingus by relationship type, derived from 1-month sexual diary data. RESULTS: Low behavioural role rigidity for masturbation and fellatio, but higher rigidity for anal intercourse and anilingus. Participants with no regular partner showed a relatively low frequency of anal intercourse, whereas those in closed relationships showed a high frequency. CONCLUSION: Although anal intercourse shows a certain degree of behavioural role rigidity, this rigidity is not large enough to conclude that gay men exclusively engage in either an active or a passive role. Typical rates for exclusive active and passive roles for anal intercourse during the month the diaries were recorded were in the range of 12-15%; the dual role was significantly higher.

The testing of saliva samples for HIV-1 antibodies: reliability in a non-clinic setting.

AIMS: To assess the reliability of saliva samples as a means of testing for HIV-antibodies outside clinic settings. METHODS: Men taking part in a non-clinic longitudinal study of homosexually active men provided samples of saliva and blood. Sera were screened using a competitive ELISA (Wellcozyme) and positive sera were confirmed by an indirect ELISA (Abbott). Saliva samples were screened either using an IgG captive radioimmunoassay or an amplified ELISA. RESULTS: A total of 534 paired saliva and blood samples were tested. Overall sensitivity was 96.2% and specificity was 100%. None of the saliva tests were falsely positive for HIV-1 antibodies. CONCLUSIONS: HIV-1 saliva tests can reliably be used in a non-clinic or field setting. However, if results are to be given to respondents, it is necessary to offer adequate counselling and consider the mechanisms for referral and follow-up for those that are found to be HIV-1 antibody positive.

No connection between alcohol use and unsafe sex among gay and bisexual men.

OBJECTIVE: To investigate the relationship between alcohol use and unsafe sexual behaviour. METHODS: The paper discusses data collected from 461 gay and bisexual men interviewed in England and Wales by Project SIGMA during 1991-1992. These data were collected during face-to-face interviews using retrospective weekly diary techniques and include details of all sexual sessions and alcohol use. The 819 reported sexual sessions with other men are divided into those that involved alcohol use (30.6%) and those that did not. RESULTS: Differences in the incidence of HIV risk behaviours between sexual sessions that involved alcohol use and those that did not are small, and none are statistically significant. Furthermore, for those men who engaged in sexual behaviour whilst under the influence of alcohol, the quantity of alcohol consumed had no effect on sexual behaviour. CONCLUSIONS: Among gay and bisexual men, sex under the influence of alcohol is no more likely to be unsafe than sex among men who have not consumed alcohol.

Changes in condom use by gay men.

Cross sectional and longitudinal data on condom use among homosexually active men is presented. Data pertain to two waves of interviewing (1987/8 and 1991) from Project SIGMA, a large longitudinal study of male homosexual behaviour in the light of HIV. Aggregate changes across the time-period indicate an increase in condom use for both insertive and receptive anal intercourse, particularly with casual partners. Condom use is still much more prevalent with casual rather than regular partners. Longitudinal analysis show considerable changes at the individual level, with almost a third of men changing their practices. Half of those decreased their risk behaviours, whilst the other half increased them. Less than 1% used condoms for fellatio in the year preceding the 1991 interview, but 8.3% had used other barriers during sex, primarily for hygiene and fun reasons, rather than as disease prophylaxis. Some implications are drawn for condom promotion and HIV prevention.

PIP: Even though the uptake of condoms by homosexual and bisexual males definitely ranks as one of the most dramatic health protective behavioral changes ever recorded, HIV prevention campaigns nonetheless continue to encourage these men to use condoms during anal intercourse. Maybe 10% of gay men used condoms prior to 1980, and then primarily for reasons of hygiene, but 78% of gay and bisexual men use them for anal intercourse by 1987 and were regularly used by 50% of all men engaging in anal sex. This paper reports changes in condom use in the only non-clinic longitudinal study of gay and bisexual) men in England and Wales. 358 men were interviewed 1987/88 and 1991, and a total of 472 men in 1991. The participants were predominantly well-educated, White, and happy with their sexuality. At the aggregate level, an increase in condom use was observed over the period for both insertive and receptive anal intercourse, especially with casual partners. Longitudinal analysis shows a lot of change at the individual level, with almost a third of the men changing their practices; half of these, however, decreased their risk behaviors, while the other half increased them. Further, less than 1% used condoms for fellatio in the year preceding the 1991 interview, but 8.3% had used other barriers such as rubber gloves and dental dams during sex mainly for hygiene and fun reasons instead of for disease prevention. The authors comment on the implications of these findings for condom promotion and HIV prevention.