The cell activation depends on T cell antigen receptor binding to antigen plus MHC and costimulation. The binding of CD28, expressed on the T cell surface to B7 (B7-1 or CD80 / B7-2 or CD86) present on the antigen-presenting cells (APCs), determines, in several T cell function models, if activation or anergy follows antigenic stimulation. In leprosy, the role of CD80 and CD86 as costimulatory signal in M. leprae-specific cellular immunity has not yet been defined. We investigated the role of B7-CD28 pathway of T cell activation in the in vitro response to M. leprae, following stimulation in the presence of monocytes or dendritic cells (DCs) as APCs. Monocytes were purified, by cold aggregation, from peripheral blood mononuclear leukocytes (PBMC), isolated from leprosy patients. In order to obtain DCs, the monocytes were cultured in the presence of IL-4 and GM-CSF. T cells were purified from PBMC by negative selection with mABs and C'. The phenotype of the cell populations was monitored by FACS. Lymphoproliferative assays were performed with T cells, in the presence of monocytes or DCs. The cells were stimulated by M. leprae in the presence of anti- CD80 antibody (Ab) and/or anti- CD86 antibody (Ab) (Innogenetics). In some experiments Il-10, Il-12 and anti-Il-12 Ab were also added to the culture. We observed a significantly more efficient APC function for DCs when compared to monocytes in T cell in vitro responses to M. leprae. Regardless of the clinical form of Leprosy, the M. leprae-specific immune response was markedly reduced in the presence of anti- CD86 Ab. Il-12 increase the immune response to M. leprae while IL-10 or anti-IL-12 Ab reduce this response when monocytes or DCs were used as APCs.
Leprosy, which was known to ancient India as “Kustha Roga” is thought to be its origin from India also. It is, still, a major public health problem in India affecting many people every year. India is, now, having maximum numbers of leprosy cases worldwide and accounts for 67% of total prevalence and 73% of total new case detection. Huge numbers of new cases have been detected in recent years (Last year new cases were 782501) because of adoption of new strategy, Modified Leprosy Elimination compaign (MLEC), and effective health education campaign. Presently, 70% of the total new caseloads of India are from five most heavily infected states. There is significant improvement in the overall situation as is evident from steady decline of prevalence rate from 38.6 cases per 10, 000 population in 1985 to 5.0 per 10, 000 in 1999.