Role of different B-cell subsets in the specific and polyclonal immune response to T-independent antigens type 2

Role of different B-cell subsets in the immune response to T-independent antigen type 2 (TI-2) was studied. BALB/c and C57BL/6 mice were immunized by polyvinylpyrrolidon (PVP), and the numbers of antibody- and Ig-forming cells (AFC and IFC, respectively) were determined by ELISPOT method. The number of cells producing non-specific Ig (nIFC) was calculated as the difference between the number of IFC and AFC; the number of nIFC induced by PVP was calculated as the difference between the number of nIFC in immune and control splenocytes. Immunization by PVP induced not only the AFC appearance, but also the increase in the number of the antigen-induced nIFC. The treatment of splenocytes by anti-CD5 antibodies and guinea pig complement reduced the increase in the numbers of newly formed AFC and nIFC to approximately 40% of control level. It means that CD5+ cells play an important role not only in the specific, but also in polyclonal immune response to non-self TI-2. To be sure that the decrease of AFC and nIFC numbers is due to depletion for CD5+ B-cells, but not CD5+ T-cells, splenocytes were separated to B-1 and B-2 subsets, and the numbers of AFC, IFC and nIFC were determined in each B-cell subpopulation separately. The overwhelming majority of newly formed AFC and nIFC was detected in B-1 subset. The numbers of AFC and nIFC in B-1 compartment was approximately 10-fold greater than in B-2 cells. A close parallelism between AFC and nIFC formation was observed. It is concluded that specific and polyclonal immune response to non-self TI-2-PVP-depends mainly on CD5+ B-1 subset.