Sven Britton

Immune Responses to the Mycobacterium tuberculosis-Specific Antigen ESAT-6 Signal Subclinical Infection among Contacts of Tuberculosis Patients

ABSTRACT Diagnosis of latent Mycobacterium tuberculosis infection is considered essential for tuberculosis control but is hampered by the lack of specific reagents. We report that strong recognition of tuberculosis complex-specific antigen ESAT-6 by healthy household contacts of tuberculosis patients correlates with the subsequent development of active tuberculosis during a 2-year follow-up period.

Cyclosporin A--usefulness, risks and mechanism of action.

Very little new happened in the field of immunosuppression after the discovery of azathioprine in the early sixties (Schwarz et al. 1959). Admittedly, there has been the introduction of heterologous antilymphocyte serum (Starzl et al. 1967), which to some extent has become a part of the regular therapeutic regimen in organ transplantation. Other than that, very little that could stop an immune response has been brought forward by the immunologists during these two past decades. Nevertheless, the understanding of immune functions has advanced a great deal during that same period, although in terms of immunosuppression the transplant surgeons were left with the old, but not so effective combination of steroids, azathoprine and somewhat later anti-lymphocyte serum (that, indeed, they still use). But a new drug is rapidly invading the market. That is cyclosporin A (CyA), which is the scope of this review. Although it was detected nearly 10 years ago (Borel 1976), it is still new as it is presently being scrutinized in clinical trials in man and is thus not commonly in use yet. In most countries it has as yet only been used for very limited purposes. The attraction of this compound is multifold, but one feature is that, unlike all other immunosuppressants, tentative mechanisms of action for it have been brought forward based on interpretable experimental data. This is, we think, why a review of the present state of knowledge on cyclosporin A is warranted. The drug has already been admirably analyzed in these reviews (Calne 1979), but much relevant information on it has accumulated since then.

Humoral and Cellular Immunity in Humans Studied at the Cell Level from Birth to Two Years of Age

Infections remain a leading cause of neonatal death in spite of improvements in public health and medical care including the use of antibiotics. The incidence of life threatening viral and bacterial infections in human newborns is much higher than in adults. Intense studies of the reasons for this have led to various and sometimes conflicting conclusions. Lack of earlier antigenic experience, intrinsic immaturity of lymphocyte functions and active cellular suppressive mechanisms, or a combination of these possibilities, are suggested explanations (Lawton et al. 1972, Stiehm 1975, Xanthou et al. 1976, Hayward & Lawton 1977, Oldstone et al. 1977, Miller 1978). Many conclusions about human B lymphocyte function in the neonate have been derived from the immunochemical analysis of immunoglobulins present in the serum of the neonate and developing infant. Such studies have been fraught with difficulty both because of the presence of passively transferred maternal IgG and its secondary interference with any attempts to induce in vivo antigenic challenge. In viiro specific antigenic responses have, with a few notable exceptions (Hoffman 1980. Saxon & Stevens 1980), proved difficult even in the adult human, probably principally because peripheral blood is the only logistic source of lymphocytes. Such studies become impossible in the neonate where even blood is available only in minimal quantities. There is, therefore, a notable absence of functional B lymphocyte studies performed on the developing human, particularly outside the immediate neonatal period. It is only with sequential cell functional studies that the process of B lymphocyte functional maturation can be clarified.

A New Approach to the Study of Human B Lymphocyte Function Using an Indirect Plaque Assay and a Direct B Cell Activator

The understanding of the human immune system has been governed by technical developments. The description of electrophoresis and immunoelectrophoresis allowed the monoclonality and class specificity of myeloma proteins to be analyzed, and the recognition of agammaglobulinaemia. The description of myelomas aided development of the clonal selection theory and the variety of agammaglobulinaemias allowed speculation about lymphoid differentiation. In the humoral limb of the immune response the next major development was the discovery of B lymphocyte surface markers (Moller 1961, Coombs et al. 1969, Dickler & Kunkel 1972), which allowed characterization of B lymphocyte populations in ontogeny, immunodeficiency and leukemias (Cooper et al. 1973, Seligmann 1973). Surface markers in resting cells have proved to be poor indicators of B cell function since many agammaglobulinaemias bear a normal complement of resting B cells which are, however, unable to synthesize immunoglobulin. Functional analysis of B lymphocyte populations in murine systems has been greatly facilitated by the use of polyclonal B cell activators (PBA) to provide a nonspecific stimulus to maturation and immunoglobulin synthesis of large number of clones and by the use of the plaque assays as a sensitive technique for detection of antibody synthesis at the cellular level. Pokeweed mitogen (PWM) has been the most studied human B cell mitogen and its use has yielded valuable information in agammaglobulinaemia and in human B lymphocyte ontogeny. Activation has been assessed by morphological blast formation, cytoplasmic immunoglobulin synthesis or released immunoglobulin

Poor immunogenicity of BCG in helminth infected population is associated with increased in vitro TGF-β production

The only vaccine available against tuberculosis (TB), BCG, so effective in experimental animal models, has been under scrutiny for a long time owing to its variable efficacy against pulmonary tuberculosis in adults. In this study, we evaluated whether anti-helminthic therapy prior to BCG vaccination could increase the immunogenicity of BCG vaccination in helminth infected population. We recruited volunteers with evidence of prior mycobacterial infection and who were asymptomatic carriers of helminths. The subjects were randomized to receive either anti-helminthic drugs or placebo. Three months later, BCG vaccination was administered to volunteers. Mycobacterial antigen-specific cytokine responses were assessed 2 months after vaccination. The results show that peripheral blood mononuclear cells obtained from the placebo group were found to have a lower frequency of IFN-gamma (129 vs 191, p=0.03) and IL-12 (149 vs 243, p=0.013) producing cells per 2 x 10(5) PBMC (peripheral blood mononuclear cells) when stimulated in vitro with a mycobacterial antigen mixture (purified protein derivative (PPD)) compared to those from the dewormed group. On the other hand the placebo group had higher frequency of TGF-beta producing cells in response to PPD (152 vs 81.3, p=0.002) or the T cell mitogen concanavalin A (Con A) (210 vs 157, p=0.03). However, no detectable IL-4 or IL-5 producing cells were observed when cells were stimulated with PPD. Comparable numbers of both cytokine producing cells were induced in both groups upon stimulation with concanavalin A (IL-4 217 vs 191, p=0.08) and IL-5 (131 vs 103, p=0.14). The data presented here demonstrate that chronic worm infection reduces the immunogenicity of BCG in humans and this was associated with increased TGF-beta production but not with enhanced Th2 immune response.

Circulating TNF-alpha, TGF-beta, and IL-10 in tuberculosis patients and healthy contacts.

Levels of tumour necrosis factor (TNF)‐α, transforming growth factor (TGF)‐β, and interleukin (IL)‐10 in plasma of pulmonary tuberculosis (TB) patients and healthy contacts and plasma and pleural fluid of patients with tuberculous pleuritis were examined by enzyme immunoassay. Plasma TNF‐α and IL‐10 were elevated to significant levels in healthy contacts. High levels of TGF‐β and IL‐10 were also detected in plasma from TB patients and healthy contacts. Pleural fluid contained all three cytokines with the level of IL‐10 being highest followed by TGF‐β and TNF‐α. Plasma of tuberculous pleuritis patients also had detectable levels of the three cytokines. Increased levels of TNF‐α in plasma of contacts and to some extent pleural fluid of pleuritis patients, is perhaps to limit the infection, while elevated IL‐10 in plasma of TB patients and contacts and pleural fluid would perhaps modulate excess proinflammation. Elevated TGF‐β in TB patients suggests its role in the immunopathogenesis.

Hiv viral load and response to antileishmanial chemotherapy in co-infected patients

OBJECTIVE To investigate whether clearance of Leishmania parasites from tissue aspirate smears in patients with HIV and visceral leishmaniasis (VL) co-infection treated with pentavalent antimonials is influenced by initial HIV viral load and to assess the effect of active VL on HIV viral load and replication in vivo. METHODS Leishmania parasites were identified in Giemsa-stained smears prepared from tissue aspirates. Parasite index was determined by quantifying Leishmania donovani bodies in smears. HIV-1 RNA was quantitated by using the nucleic acid sequence-based amplification technique with a limit of detection of 500 copies/ml. All patients were treated with pentavalent antimonials at 20 mg pentavalent antimony (Sb(V))/kg daily for a total of 28 days. None of the patients received specific anti-retroviral therapy. RESULTS Seventeen patients (73.9%) showed good initial response to anti-leishmanial treatment and the remaining six (26.1%) had very poor response. Among the good responders, 11 (64.7%) had no demonstrable Leishmania donovani bodies in post-therapy tissue aspirate smear preparations, and in the remaining six (35.3%) their parasite loads were reduced to very low levels. Patients with poor response had persistently high parasite index despite completion of anti-leishmanial chemotherapy. Poor responders had pre-treatment median HIV viral load that was >160-fold higher than responders to anti-leishmanial chemotherapy; [410000 copies/ml (quartile range, 33000-530000) and 2500 copies/ml (quartile range 500-297500), respectively]. Furthermore, compared with pre-treatment viral concentrations, patients with good response showed marked reduction in post-treatment viral load. In contrast, post-treatment HIV viral concentrations were markedly increased among patients with poor response to anti-leishmanial therapy. CONCLUSIONS The results suggest that pre-treatment HIV viral load influences response to anti-leishmanial chemotherapy and active VL is associated with increased viral replication in vivo, supporting the notion that dual infection plays an important role in the pathogenesis and disease progression of either infection.

Are intestinal helminths risk factors for developing active tuberculosis

Objectives  To determine the prevalence of intestinal helminth infections in active tuberculosis patients and their healthy household contacts and to assess its association with active TB in an area endemic for both types of infections.

Low dose chronic Schistosoma mansoni infection increases susceptibility to Mycobacterium bovis BCG infection in mice

The incidence of mycobacterial diseases is high and the efficacy of Bacillus Calmette Guérin (BCG) is low in most areas of the world where chronic worm infections are common. However, if and how concurrent worm infections could affect immunity to mycobacterial infections has not been elucidated. In this study we investigated whether infection of mice with Schistosoma mansoni could affect the ability of the animals to control Mycobacterium bovis BCG infection and the immune response to mycobacterial antigens. BALB/c mice subclinically infected with S. mansoni were challenged with M. bovis BCG via the intravenous route. The ability of the animals to contain the replication of M. bovis BCG in their organs, lung pathology as well as the in vitro mycobacterial and worm antigen induced immune responses were evaluated. The results showed that S. mansoni coinfected mice had significantly higher levels of BCG bacilli in their organs and sustained greater lung pathology compared to Schistosoma uninfected controls. Moreover, Schistosoma infected mice show depressed mycobacterial antigen specific Th1 type responses. This is an indication that chronic worm infection could affect resistance/susceptibility to mycobacterial infections by impairing mycobacteria antigen specific Th1 type responses. This finding is potentially important in the control of TB in helminth endemic parts of the world.

Chronic helminth infections may negatively influence immunity against tuberculosis and other diseases of public health importance

Tuberculosis (TB) has once again become a major public health threat owing to the combined effects of deteriorating socioeconomic situations and the emergence of the HIV/AIDS pandemic. The only vaccine available against TB, although effective in reducing the burden of childhood TB, shows enormous variability in its efficacy against pulmonary TB, which is the most common form of the disease in adults. Most areas of high TB incidence and poor TB vaccine efficacy have a high prevalence of intestinal helminth infections. Such infections have been shown to cause a range of immunomodulation characterized by enhanced T helper 2-type cytokine profile, high immunoglobulin E levels and upregulated regulatory T-cell activity, as well as chronic immune activation. An altered background immune profile could have adverse effects on the outcome of subsequent infections and vaccinations. In support of this hypothesis, studies conducted in animals and humans living in worm-endemic areas have shown that helminths impair resistance against a number of infections of major public health importance, including TB, malaria and HIV/AIDS. Understanding such interactions could assist in the design of vaccines against these diseases.