Biological characterization of an immunosuppressant from group A streptococci

Effect of Peptidoglycan-Polysaccharide Complex on Reproductive Efficiency in Sheep

PROBLEM

Spontaneous mastitis or induced infections mimicking mastitis reduce pregnancy rates in ruminants. The effect of immunization with either a mastitis-related pathogen component, peptidoglycan-polysaccharide (PG-PS), or killed Streptococcus pyogenes on pregnancy outcome was investigated.

METHOD OF STUDY

Ewe lambs were immunized with PG-PS (n = 50) or killed bacteria (n = 50) or were not immunized (control, n = 100). Titers of PG-PS immunoglobulin G (IgG) were detected by enzyme-linked immunosorbent assay (ELISA). Ewes were bred by rams at synchronized estrus. All immunized ewes and half of the ewes not immunized were challenged with PG-PS on day 5 after breeding. Pregnancy maintenance was evaluated.

RESULTS

Although the proportion of ewes pregnant at day 42 after breeding did not differ among treatments, the probability of pregnancy decreased with total dose of PG-PS (P < 0.05).

CONCLUSIONS

Immunization of ewe lambs with PG-PS or killed S. pyogenes did not improve pregnancy maintenance. Furthermore, the toxic streptococcal component decreased pregnancy rate in immunized sheep in a dose-dependent manner.

Treponema denticola immunoinhibitory protein induces irreversible G1 arrest in activated human lymphocytes

Oral spirochetes may contribute to the pathogenesis of a number of disorders including periodontal and periradicular diseases; however, the mechanism (s) by which these organisms act to cause disease is unknown. We have previously shown that extracts of the oral spirochete, Treponema denticola, contain an immunosuppressive protein (Sip) which impairs human lymphocyte proliferation. The objective of this study was to determine the mechanism by which Sip alters the proliferative response of lymphocytes. Human T-cells were activated by PHA in the presence or absence of Sip and cell cycle progression was assessed by flow cytometry. Cell cycle distribution was based upon DNA, RNA and protein content as well as expression of the activation markers; CD69 and IL-2R. Seventy-two hours following activation with PHA, cells were found in the G0, G1, S and G2/M phases of the cell cycle. In contrast, pretreatment with Sip resulted in a significant reduction of cells in the S and G2/M phases and a concomitant increase in the G1 phase. Sip did not alter the expression of the early activation markers CD69 and CD25R. To determine if G1 arrest resulted in activation of the checkpoint and cell death, we also monitored Sip-treated cells for apoptosis. Indeed, treatment with Sip resulted in both DNA fragmentation and caspase activation after 96 h. Our results indicate that Sip induces G1 arrest in human T-cells and, furthermore, that the arrest is irreversible, culminating in activation of the apoptotic cascade. We propose that if cell cycle arrest occurs in vivo, it may result in local and/or systemic immunosuppression and thereby enhance the pathogenicity of spirochetes and/or that of other opportunistic organisms.

Immunologic dysfunction in the pathogenesis of periodontal diseases

Despite significant progress in our understanding of the pathogenesis and etiology of periodontal diseases, the nature and contribution of the immune system to this disorder remains unclear. Several studies provide evidence for either a protective or destructive rôle. These conflicting findings are difficult to reconcile, since most interpretations tend to argue for a static contributory rôle (i.e., either protective or destructive) of the immune system. Current theories on the rôle of the immune response do not address these conflicting findings as well as the contradictory observation of a detectable immune response in the face of persistent infection in these patients. In this article, we present a model, based on available data, for the contribution of the immune system to the pathogenesis of periodontal disease. This model ascribes a dynamic rôle for the immune response. As documented in other infectious diseases, it is entirely possible, for example, that a state of immunologic dysfunction may occur in the earliest stages of periodontal disease progression; this may then be followed by a period of active immune reactivity (humoral and/or cellular) that would represent either a delayed or depressed response. This model is discussed in conjunction with recent findings that several suspected periodontal pathogens are capable of producing immunosuppressive agents. Many of the apparently contradictory clinical observations concerning the host immune response to oral pathogens and its correlation (or lack of) with both the progression and severity of periodontal disease may be accounted for in this model.

Suppressive action of cytoplasmic and metabolite extracts of Candida albicans on the immune response in guinea pigs

This study investigated the possibility that Candida albicans components exert a suppressive effect on the immune response of guinea pigs (GP), similar to that of live C. albicans organisms as was previously shown. Hartley GP were inoculated with C. albicans crude cytoplasmic or metabolite (culture filtrate) extracts (containing most of the organism's cell contents or its metabolite and degradation products, respectively). Their immunological responses towards sheep red blood cells (SRBC) were compared with those of GP inoculated with SRBC alone or with SRBC together with live C. albicans organisms. The immunological responses were measured by: 1) rosette formation (RF) of SRBC with peritoneal macrophages, 2) haemolytic plaque formation (PFC) with lymph node-cells, 3) haemagglutination and 4) haemolysis tests. According to the RF tests, inoculation of GP with either cytoplasmic or metabolite extracts resulted in decreased RF as compared to GP inoculated with SRBC only; the decrease was correlated with the protein concentration of the extracts. Inoculation with metabolite extract led to a more diminished RF than with cytoplasmic extract, but less than with live C. albicans organisms. Inoculation of cytoplasmic extracts did not affect the haemagglutinin and haemolysin titers, while that of metabolite extracts resulted in a slight decrease of these titers. The assays for PFC were not conclusive enough to point to a suppressive effect of C. albicans extracts. In summary, it appears that both the cytoplasmic and metabolite extracts of C. albicans exert a partial suppressive effect on the immune response in GP, as judged primarily on the basis of the RF results.

Recent advances in rheumatic fever control and future prospect: a WHO memorandum

The public health importance of rheumatic fever is not directly related to its prevalence but is a complex function of many factors, such as incidence, prevalence, mortality, disability, and cost to the community, all relative to the importance of other diseases. Although the prevalence is low and still decreasing in developed countries, rheumatic fever is the commonest form of heart disease in many developing countries. Advances in the bacterial and serological characterization of group A streptococci are reviewed in this Memorandum, with emphasis on the nature of the structural elements of the cell wall. Microbiological methods play an important role in the diagnosis and control of rheumatic fever and up-to-date information is given concerning methods of isolation and grouping and of typing. Methods of assessing streptococcal activity in the host, in particular the different antibody responses found in relation to different pathological conditions, are discussed, as are the improvements required in laboratory services to enable them to carry out these duties adequately. Current concepts concerning the pathogenesis of rheumatic fever are reviewed together with differences in the epidemiology related to the different sites of infection and the problems of carriership. The Memorandum is also concerned with the methods of prevention and treatment, including prevention of recurrences, control of the disease in communities, and strategies for nationwide control.

Stimulation of cAMP levels and modulation of antibody formation in mice immunized with cholera toxin

Injection of mice with 1.0 mu g of a purified exotoxin derived from Vitro cholerae together with a challenge injection of sheep erythrocytes (SRBC)P OR E. coli LPS markedly influenced the immune response to these antigens. Simultaneous injection of the toxin with antigen resulted in a delayed appearance of antibody-forming cells during the first few days after immunization, followed by a marked enhancement of the peak numbers of antibody-forming cells. In the case of the immune response to SRBC, both 19S and 7S plaque-forming cells (PFC) were enhanced on the peak day of response after simulataneous immunization of toxin-injected mice. The secondary immune response to SRBC was also similarly affected when cholera toxin was given along with a second injection of erythrocytes: i.e. a delay in appearance of the first antibody-forming cells followed by a marked enhancement of the peak 19S and 7S PFC response. Injection of cholera toxin 103 days prior to SRBC or LPS was immunosuppressive. The effect of cholera toxin on the level of splenic cyclic AMP appeared related to the effects on antibody formation.

Decreased reactivity of lymphocytes in mixed-leukocyte culture from patients with rheumatic fever

The purpose of this study was to evaluate cellular immune responsiveness. in patients with acute rheumatic fever (ARF). Peripheral blood lymphocytes were obtained for culture from patients who had ARF within the past 2-3 months. No patient was receiving steroids at the time of the study. Peripheral lymphocytes were also obtained from normal control individuals.

Lymphocyte cultures were maintained for 7 days in minimum essential medium with 10% fetal calf serum in a 5% CO 2 environment. Cellular responsiveness was checked concomitantly with pokeweed mitogen and/or phytohemagglutinin. Mixed-lymphocyte cultures were studied between patients with ARF and between patients with ARF and normal controls. Normal responses were arbitrarily defined as a threefold increase over baseline counts.

ARF cells were capable of stimulating other ARF cells in only three of 14 instances and were able to stimulate control cells in only three of 11 studies. Conversely, ARF lymphocytes were capable of being stimulated by control normal cells in five of 10 experiments. Thus decreased cellular responsiveness and abnormalities in cellular immunity are present in many patients with ARF, since lymphocytes from patients with ARF are usually incapable of stimulating normal or other ARF cells. However, ARF cells are capable of being stimulated by normal control cells in 50% of studies performed.