Immunology of tuberculosis

Tuberculosis is a major health problem throughout the world causing large number of deaths, more than that from any other single infectious disease. The review attempts to summarize the information available on host immune response to Mycobacterium tuberculosis. Since the main route of entry of the causative agent is the respiratory route, alveolar macrophages are the important cell types, which combat the pathogen. Various aspects of macrophage-mycobacterium interactions and the role of macrophage in host response such as binding of M. tuberculosis to macrophages via surface receptors, phagosome-lysosome fusion, mycobacterial growth inhibition/killing through free radical based mechanisms such as reactive oxygen and nitrogen intermediates; cytokine-mediated mechanisms; recruitment of accessory immune cells for local inflammatory response and presentation of antigens to T cells for development of acquired immunity have been described. The role of macrophage apoptosis in containing the growth of the bacilli is also discussed. The role of other components of innate immune response such as natural resistance associated macrophage protein (Nramp), neutrophils, and natural killer cells has been discussed. The specific acquired immune response through CD4 T cells, mainly responsible for protective Th1 cytokines and through CD8 cells bringing about cytotoxicity, also has been described. The role of CD-1 restricted CD8+ T cells and non-MHC restricted g/d T cells has been described although it is incompletely understood at the present time. Humoral immune response is seen though not implicated in protection. The value of cytokine therapy has also been reviewed. Influence of the host human leucocyte antigens (HLA) on the susceptibility to disease is discussed. Mycobacteria are endowed with mechanisms through which they can evade the onslaught of host defense response. These mechanisms are discussed including diminishing the ability of antigen presenting cells to present antigens to CD4+ T cells; production of suppressive cytokines; escape from fused phagosomes and inducing T cell apoptosis. The review brings out the complexity of the host-pathogen interaction and underlines the importance of identifying the mechanisms involved in protection, in order to design vaccine strategies and find out surrogate markers to be measured as in vitro correlate of protective immunity

Isolation and Evaluation of Diagnostic Value of Two Major Secreted Proteins of Mycobacterium Tuberculosis

Two secreted antigens of Mycobacterium tuberculosis, namely the antigen 85 complex (30/31) and 38kDa antigens, were purified from the whole culture filtrate by using two dimensional preparative electrophoresis and anion exchange chromatography, respectively. Individual components of the antigen 85 complex namely, antigen 85A, 85B and 85C, were separated using hydrophobic interaction chromatography. The humoral antibody activity to these antigens in sputum positive cases of active pulmonary tuberculosis and normal healthy volunteers was determined by enzyme linked immunosorbent assay (ELISA) and immunoblot. Recombinant 38kDa and antigen 6 were used as reference antigens for the assay. None of the healthy volunteers reacted with the 38kDa antigen, while 52% of the TB sera reacted with it. Of the three components of the antigen 85 complex, 85B gave the highest positivity of 40 per cent. The results of combination of 38kDa with antigen 6 offered better results with 76% positivity

Age-related changes in blood lymphocyte subsets of south Indian children

Background. Enumeration of lymphocyte subsets has been widely used for the diagnosis and monitoring of several haematological and immunological disorders. Various studies have demonstrated age, sex and racial differences in lymphocyte subset expression. Reference values are not available for Indian children and there is a need for this information to replace commonly used, but inappropriate, adult lymphocyte subset ranges. Methods. One hundred thirty-eight healthy children be tween 3 and 15 years of age, attending a local government school in Chennai, South India were included in the study. Haemoglobin levels, and total and differential cell counts were determined using an automated counter and lymphocyte subsets were analysed by flowcytornetry. Results. The mean (SD) absolute lymphocyte count declined with age from 4338 (1031) at 3 years to reach a plateau of 3096 (914) at 11-13 years (p < 0.05). A significant decline was also observed in the absolute numbers of CD3+, CD4+, CD8+ and CD19 + cells. However, the percentage values of CD3+, CD4+, CD8+, CD16/56+ cells and the CD4/CD8 ratio remained fairly stable across the age range. Conclusion. Our data would prove useful in interpreting disease-related changes in lymphocyte subsets in Indian children of different age groups. Age-related decrease in the absolute lymphocyte count as well as numbers of CD4 and CD8 cells was found to occur between the ages of 3 and 11 years. A normogram relating age to CD4 count has been developed

Comparison of whole blood and PBMC assays for T-cell functional analysis

BACKGROUND: Tuberculosis remains the foremost cause of morbidity and mortality, more than any other single infectious disease in the world. Cell mediated immune response plays a crucial role in the control of tuberculosis. Therefore, measuring cell mediated immune response against the antigens is having a vital role in understanding the pathogenesis of tuberculosis, which will also help in the diagnosis of and vaccination for tuberculosis. FINDINGS: The aim of the present study was to compare and optimize the assay conditions to measure the cell mediated immune response against M. tuberculosis specific antigens. Because the conventional PBMC assays (due to requirement of large volume of blood sample) are unable to screen more number of antigens within the same blood sample. So, here we have compared 6 days culture supernatants of 1:5 and 1:10 diluted blood and PBMCs from healthy laboratory volunteers, to assess the proliferative response of T lymphocytes and secreted IFN-γ levels against purified recombinant antigen of M. tuberculosis (MPT51, Rv3803c), crude antigens of M. tuberculosis (PPD) and mitogen (PHA). CONCLUSIONS: We have observed good correlation between each assay and also the mean difference of these assays did not reach the statistical significance (p > 0.05). From these results, we conclude that 1:10 diluted whole-blood cultures can be well-suited as an alternative assay to measure cytokine production and lymphocyte proliferation in comparison to the conventional PBMC assays. Moreover, 1:10 diluted blood assays require less volume of blood when compared to PBMC assays which will be useful particularly in paediatric and field studies in endemic countries, where blood volume is a limiting factor

Cell-mediated immunity in chyluria

Cellular immune response to mitogens phytohemaggluthin (PHA) and poke weed mitogen (PWM) was assessed in 13 patients with chyluria and 32 healthy controls. The mean stimulation Index of the patient group was significantly lower than the control group. The degree of depression was neither related to the duration of excretion of chyle nor to the microfilaraemic status

Role of Interferon Gamma Release Assay in Active TB Diagnosis among HIV Infected Individuals

immunodeficiency virus (HIV) infected individuals. In this study, we assessed the sensitivity of Interferon gamma release assay (IGRA) in active tuberculosis patients who were positive for HIV infection and compared it with that of tuberculin skin test (TST). Methodology/Principal Findings: A total of 105 HIV-TB patients who were naı¨ve for anti tuberculosis and anti retroviral therapy were included for this study out of which 53 (50%) were culture positive. Of 105 tested, QuantiFERON-TB Gold intube (QFT-G) was positive in 65% (95% CI: 56% to 74%), negative in 18% (95% CI: 11% to 25%) and indeterminate in 17% (95% CI: 10% to 24%) of patients. The sensitivity of QFT-G remained similar in pulmonary TB and extra-pulmonary TB patients. The QFT-G positivity was not affected by low CD4 count, but it often gave indeterminate results especially in individuals with CD4 count ,200 cells/ml. All of the QFT-G indeterminate patients whose sputum culture were positive, showed #0.25 IU/ml of IFN-c response to phytohemagglutinin (PHA). TST was performed in all the 105 patients and yielded the sensitivity of 31% (95% CI: 40% to 22%). All the TST positives were QFT-G positives. The sensitivity of TST was decreased, when CD4 cell counts declined. Conclusions/Significance: Our study shows neither QFT-G alone or in combination with TST can be used to exclude the suspicion of active TB disease. However, unlike TST, QFT-G yielded fewer false negative results even in individuals with low CD4 count. The low PHA cut-off point for indeterminate results suggested in this study (#0.25 IU/ml) may improve the proportion of valid QFT-G results

HLA-DR phenotypes and IgG, IgA and IgM antibody responses to Mycobacterium tuberculosis culture filtrate and 30 kDa antigens in pulmonary tuberculosis

The role of HLA-DR genetic make-up on the IgG, IgA and IgM antibody response to Mycobacterium tuberculosis culture filtrate and 30 kDa antigens was studied in pulmonary tuberculosis. The study was carried out in HLA-DR typed active pulmonary tuberculosis (ATB) patients (n = 37), inactive (cured) pulmonary tuberculosis (ITB) patients (n = 79) and normal healthy subjects (NHS; n = 46). In ATB and ITB (cured) patients, IgG antibody (optical density at 490 nm for 1 : 3200 dilution) as measured by enzyme-linked immunosorbent assay was the predominant one than IgA and IgM antibodies. Increased IgG antibody titre to culture filtrate (P = 0.03) and decreased titre to 30 kDa antigen were observed with HLA-DR1-positive ATB patients than non-DR1 (ATB) patients. Moreover, HLA-DR4- and HLA-DR6-positive ATB patients showed trends toward an increased IgG antibody response to 30 kDa antigen than HLA-DR4- and HLADR6- negative (ATB) patients respectively. Significantly increased IgA antibody to 30 kDa antigen was observed with HLA-DR1-positive ATB patients than non-DR1 patients (P = 0.03). The study suggests that multiple HLA-DR molecules may regulate the IgG and IgA antibody responses to various proteins of M. tuberculosis. Moreover, HLA-DR phenotypes and increased IgG and IgA antibody titres may be useful to differentiate M. tuberculosis-infected subjects from normal subjects and cured patients with the same HLA-DR phenotypes or genetic make-up