Role of complement activation and antibody in the interaction between Mycobacterium tuberculosis and human macrophages.

Mycobacterium tuberculosis-specific antibodies possess immunomodulatory effects during tuberculosis infection. Prior sensitization to environmental mycobacteria is known to suppress immune responses against BCG and M. tuberculosis. Mycobacteria-induced antibodies can influence events such as complement activation and phagocytosis during infectious process. In the present study role of anti-M. tuberculosis IgG (anti-M. tb IgG) antibody during interaction between M. tuberculosis and human macrophages mediated through complement has been examined in vitro. Anti-M. tb IgG antibody significantly enhanced complement activation by M. tuberculosis. Phagocytosis of M. tuberculosis by macrophages increased significantly in the presence of complement and/or antibody. Moreover, antibody enhanced phagocytosis in the presence of complement. Addition of antibody alone or in combination with complement also augmented intracellular viability of bacilli within macrophages. Results of this study showed that anti-mycobacterial antibody enhances complement activation and anti-M. tb IgG antibody probably modulates effects of complement during early stages of tuberculosis infection.

Serum C3d levels in tropical pulmonary eosinophilia.

Background & objectives: Results of earlier studies to evaluate the possible role of complement system in tropical pulmonary eosinophilia (TPE) using classical methods like serum haemolyte component CH50, C3 and C4 levels were inconclusive. In this study we determined levels of serum C3d which is a catabolic fragment of C3, to find out any direct evidence of activation of the complement system in TPE. Methods: The study population consisted of 3 groups. Group A consisted of 37 patients with well characterized TPE. In group B, 26 patients with pulmonary eosinophilia had similar respiratory and haemotological features as in Group A but had associated worm infestation in stool. The control group consisted of 39 healthy volunteers. Serum C3d levels were determined by sandwich ELISA technique. Results: The serum C3d levels in TPE patients were not significantly different from those of the patients of group B or the normal controls. Interpretation & conclusions: Absence of significant change in serum C3d goes against the possibility of complement activation in TPE. Results of our study suggest that complement system is unlikely to play a pivotal role in pathogenesis of TPE.

Biochemical & histochemical changes relating to fibrosis following infection with Mycobacterium tuberculosis in the guinea pig.

Guinea pigs infected with M. tuberculosis were studied for parameters relating to fibrosis following infection. The infected animals were followed up to a period of 44 wk and the changes that occurred in the lung, liver and spleen were studied. Corresponding tissues from animals injected with bleomycin, an anti-mitotic drug which has the ability to produce pulmonary fibrosis, served as positive controls. Tissue collagen, elastin and hexosamines were estimated biochemically. The presence of granuloma and stainable collagen in paraffin sections of these tissues was also studied. Establishment of the infection was assessed bacteriologically by culturing the viable organisms from the spleen. It was observed that a self-limiting infection was established in the guinea pigs and none of the animals died of the infection. In the infected animals, collagen, elastin and hexosamines showed an initial decrease followed by an increase. While the elastin and the hexosamine levels returned to the basal levels in all the three organs, collagen levels increased in the lung and were comparable to those of the bleomycin control. Collagen stainable by Van Gieson's method was found to be increased in the lung from the 4th wk onwards. The present report indicates the potential of adopting this system for studying mechanisms of fibrogenesis in tuberculous infection.

The clearance of tubercle bacilli & mycobacterial antigen vis a vis the granuloma in different organs of guinea pigs.

In the present study, an attempt was made to define the relationship of intact tubercle bacilli and/or their antigenic fragments to a granuloma in the guinea pig in order to distinguish an active from a resolving granuloma. In one set of animals, granuloma was induced in the skin by injecting heat-killed Mycobacterium tuberculosis intradermally and in another set, granuloma was produced in the lung and spleen by injecting live M. tuberculosis intramuscularly. The animals were sacrificed at various time points and skin, lung and spleen from the two groups were subjected to histological examination for the presence of granuloma, bacilli and antigenic fragments. In the dermal lesion, intact acid fast bacilli were cleared first by day 42 followed by the removal of their antigenic fragments by day 63 and finally by day 84, the granuloma had resolved completely. In the guinea pigs infected with live M. tuberculosis, removal of the bacilli followed by the clearance of antigen was observed. Though the granuloma itself did not subside completely in these animals, it was found that there was a reduction in congestion and oedema of the granulomatous area. It is concluded from the results that the demonstration of antigen at the site of lesion may be potentially useful to discriminate between a persisting and a resolving tuberculous granuloma.

A histological spectrum of host responses in tuberculous lymphadenitis.

A total of 446 lymph node biopsy specimens showing histological evidence of tuberculosis were classified into four groups based on the organization of the granuloma, the type and numbers of participating cells and the nature of necrosis. These were, hyperplastic (22.4%)--a well-formed epithelioid cell granuloma with very little necrosis, reactive (54.3%)--a well-formed granuloma consisting of epithelioid cells, macrophages, lymphocytes and plasma cells with fine, eosinophilic caseation necrosis, hyporeactive (17.7%)--a poorly organized granuloma with macrophages, immature epithelioid cells, lymphocytes and plasma cells and coarse, predominantly basophilic caseation necrosis and nonreactive (3.6%)--unorganized granuloma with macrophages, lymphocytes, plasma cells and polymorphs with non caseating necrosis. Though the number of bacilli in the sections differed in each group, there were no differences in culture positivity, Mantoux reaction or the clinical features. It is likely that the spectrum of histological responses seen in tuberculous lymphadenitis is the end result of different pathogenic mechanisms underlying the disease.

A sequential study of circulating immune complexes, complement and immunoglobulins in borderline tuberculoid leprosy patients with and without reactions.

Sequential estimates of the levels of circulating immune complexes (CIC), complement catabolic fragment C3d, complement-mediated immune complex solubilization (CMS) and immunoglobulins were made in 24 newly diagnosed with borderline tuberculoid leprosy over a 20 month period after initiation of chemotherapy. Fourteen of these patients had not suffered from reversal reactions either at the time of presentation or during the follow-up. The levels of CIC were evaluated in them from the third to the eleventh month after starting chemotherapy and immunoglobulin G (IgG) levels were evaluated up to eight months. The concentrations of C3d and immunoglobulins A (IgA) and M (IgM) were normal in these patients. The other ten patients had reversal reaction at the time of diagnosis which subsided by the third month after starting treatment. They did not have reversal reactions later. The levels of CIC and IgG were elevated and those of CMS were depressed throughout the study period. Serum C3d level was initially elevated but came down to normal by the third month while IgA and IgM levels were within normal limits. The relevance of these findings to the genesis of reversal reaction is discussed in this communication.

Histological and immunological correlates of suspected leprosy lesions.

Thirty-two subjects with suspected leprosy lesions were investigated to assess various modalities of sensibility and sweat function and these were correlated with immunological and histological parameters. It was found that pain and temperature, mediated by small unmyelinated fibres were impaired in the early lesions. Impairment of sweat function was seen only when one of the modalities of sensibility was also affected. Antibodies specific to a protein (35 kDa) antigen and phenolic glycolipid 1 of Mycobacterium leprae were positive in nine and 12 cases respectively, while 15 of the 31 biopsies revealed the presence of mycobacterial antigens in these lesions. The implications of these findings are discussed.

Studies on healthy contacts of leprosy patients--a preliminary report.

91 healthy contacts of leprosy patients were studied for subclinical infection and possibly the pre-clinical stage of the disease using a battery of tests. It was observed that the test based on competitive inhibition of monoclonal antibody binding to the MY2 a determinant of M. leprae identifies a preclinical stage of the disease.

Synovial swellings over wrist in leprosy.

Soft cystic swellings are noticed in leprosy patients during the course of disease and are seen all through the spectrum. The commonest site for these is the dorsum of wrist. At times these are seen over the dorsum and the lateral aspects of ankle as well. These contain straw colored sticky but clear fluid. On exploration these appear to arise from the synovial covering of the extensor tendons of wrist and fingers and have no communication with the wrist joint. Histology of the synovium suggests these swellings to be of inflammatory nature.