Immunoglobulin profile in pulmonary tuberculosis.
In recent years, with the advent of sophisticated immunological techniques, immunology of tuberculosis has become a subject of growing interest. The significance of delayed hypersensitivity in tuberculosis as a protective immunity has been widely discussed., Humoral response of the hosts to mycobacterial antigens depends upon the production of different types of antibodies (immunoglobulins) and is the expression of the functional capacity of immunoglobulin producing cells.
Very few studies have been reported in Indian literature regarding the significance of immunoglobulins in patients of pulmonary tuberculosis., Therefore, the present study was undertaken with the aim to have further knowledge of humoral response in patients of pulmonary tuberculosis by estimating various immunoglobulins.
The material for the study was selected from healthy human volunteers as control and from patients of pulmonary tuberculosis who were admitted in T.B. & Chest Hospital, Bikaner. Twentyfive volunteers of the control group were of good health and gave no history of previous illness relating to respiratory or liver diseases. Fifty patients having clinical, radiological and bacteriological evidence of active pulmonary tuberculosis were taken up for the study. Both the volunteers and patients belonged to different age groups between 15 and 60 years. Staging of cases of pulmonary tuberculosis was done as minimal, moderately advanced, and far-advanced according to the criteria laid down by National Tuberculosis Association of U.S.A.
The quantitative estimation of various immunoglobulins (IgG, IgA., IgM) in sera of patients and healthy individuals were carried out by single radial immuno-diffusion technique of Mancini et al as described by Fahey and McKelvey.
The various dilutions of standard immunoglobulin classes were charged to anti IgG, anti IgA and anti IgM serum agar plates along with the test proper so as to provide homogenous conditions to estimate the relative radial diffusion diameter of the precipitate produced by various concentrations of the standard immunoglobulin classes. The precipitin ring diameter in mm and immunoglobulin concentration in mg/ml were plotted on semi log 2 scale x mm graph paper. A regression straight line was drawn by joining the points by covering the maximum number as well as keeping in view of the relative distance of points left on either side.
Serum samples of patients and healthy individuals were taken for quantitation of various immunoglobulins and the single radial immuno-diffusion ring diameters were measured in mm by immunomeasure scale in all three plates having anti IgG, anti IgA and anti IgM serum and proportional levels of IgG, IgA and IgM in mg/ml were estimated against their ring diameters by standard graph plotted for IgG, IgA and IgM.
[Table 1] shows that the levels of IgG and IgA were significantly (p < 0.001) higher in patients of pulmonary tuberculosis when compared to healthy subjects. The mean value of IgM was slightly more in patients than in healthy individuals, but the difference was not statistically significant. The mean value of IgA in females was significantly (p < 0.001) higher when compared with males, while the mean values of IgG and IgM were statistically insignificant.
[Table 2] shows that the mean levels of IgG, IgA and IgM were significantly higher in Stage II when compared with Stage I. Mean levels of IgG and IgA were also significantly higher in Stage III when compared to Stage I.
[Table 3] revealed that the mean values of IgG were higher in patients with exudative and cavitary lesions when compared to those with fibro-productive or fibro-cavitary disease, but the difference was not statistically significant. The mean values of IgA and IgM had no significant relation with the nature of the disease.
Diagnosis of pulmonary tuberculosis is mainly based upon the clinical, radiological and bacteriological evidence. A serologic diagnostic test, particularly if applicable on a large scale, would have considerable and obvious advantages. It has been shown in previous studies that a high proportion of patients with tuberculosis has significantly increased levels of antibody to mycobacterium tuberculosis by using "enzyme-linked immunosorbant assay".
In the present study, the values of IgG and IgA were significantly higher in patients of pulmonary tuberculosis when compared with healthy subjects, while IgM was not significantly raised. Similar results have also been reported.,,, Fahey and McKelvey reported significant increase of IgG concentration without significant change in IgA and IgM levels in Caucasian tuberculous patients. Daniel and Baum and Bradley et al reported significantly increased level of IgG with low titers of IgM in patients of pulmonary tuberculosis.
In our study, the levels of IgA were significantly more in females than males, whereas IgG and IgM have no significant relation with sex. Faulkner et al reported increased level of IgM in females than males in both negroes and Caucasians. Our observations are different from Alarcon-Segovia and Fishbein who observed no significant difference in the level of any of the three immunoglobulins in relation to sex among patients of pulmonary tuberculosis.
In our study, the levels of IgG, IgA were significantly increased in moderate and far-advanced cases when compared to patients having minimal lesion, though the results are not appropriately comparable as the number of cases in the minimal and moderately advanced groups were very few as compared to far-advanced, the reason being that most of the hospitalised patients had far-advanced disease during study period. Jha et al reported no definite relation of various levels of immunoglobulins with increasing severity of disease. An increase in the level of IgA in relation to the extent of disease was observed by Skvor et al. There was no definite relationship in the levels of IgG, IgA and IgM with the nature of disease in the present study.
The rise of total IgG and IgA levels in patients of pulmonary tuberculosis was interpreted as humoral response to mycobacterial antigens as suggested by Skvor et al, while Grange et al observed no correlation between the levels of various immunoglobulins and the antimycobacterial antibody levels. Therefore, it is more likely that a much less specific stimulation of immunoglobulin synthesis is occurring possibly due to adjuvant activity of mycobacteria. The reason for the predominant increase in IgA is not clear. It is, however, likely that the lung which is the usual site of tuberculous lesion is known to contain a high proportion of IgA producing immune cells as suggested by South et al.
Jha et al suggested that insignificant increase in IgM could be attributed to the fact that more than 80% of their cases had cavitary lesions signifying post-primary disease and the patients exhibited a secondary response by synthesizing more IgG. This contention is supplemented by experimental studies of Daniel and Baum I who observed that IgM appears in the sera of animals as a primary response followed by IgG as a secondary event.