Model System to Study Cell Interactions and Mechanisms of Immune Response to T-Independent Type 2 Antigens in vitro

Cellular mechanisms of immune response to T-independent antigens of type 2 (TI-2 antigens) are not fully elucidated. To study the role of different lymphocyte subpopulations in this process the system of induction of immune response in vitro is most convenient. However, in vitro model for such experiments requires relatively large quantities of lymphocytes to create necessary cell density in the cultures. It hampers the study of minor lymphocyte subpopulations like CD5+ B-1 splenocytes, which play the main role in the immune response to TI-2 antiges in vivo. The problem may be resolved by the use of the mixture of cells from normal and immunodeficient congenic mice. In our experiments immune response to T-independent antigens of type 1 (TI-1 antigens) and TI-2 antigens was studied in the mixture of lymphocyte from normal (C BA) and xid CBA/N mice. CBA/N mice lack CD5+ B-1 cells and do not respond to TI-2 antigens. Therefore, their splenocytes can be used as "filler" cells to create optimal cell density in the cell cultures. Thus, CBA spleen and peritoneal cells as well as B-1 and B-2 lymphocytes isolated from them were cultured in different proportions with CBA/N splenocytes with or without antigens. LPS and polyvinylpirrolidone (PVP) were used as TI-1 or TI-2 antigens, respectively. Antibody- and immunoglobulin-forming cells (AFC and IFC, respectively) were determined on the 4-th day of cultivation by ELISPOT method. It was shown that CBA and CBA/N cells in mixed cell cultures retained their functional activity. Splenocytes of CBA mice responded to both T-independent antigens (LPS and PVP) while, CBA/N splenocytes responded to TI-1 antigens (LPS) only. It means that in vitro as in vivo B-1 cells play the main role in the immune response to TI-2 antigens. The developed model system can be used to study cellular mechanisms of the immune response to TI-1 and TI-2 antigens in vitro.