Role of Dendritic Cells in Immune Response to T-Independent Type 2 Antigens

Dendritic cells (DC) belong to the most effective antigen-presenting cells. Their role in the presentation of thymus-depending antigens and in the initiation of the primary immune responses is well established. At the same time, the participation of DC in the immune response to T-independent type 2 antigens (TI-2 antigens) is unclear. In this work, the ability of DC to initiate the immune response to polysaccharide TI-2 antigen alpha(1 -> 3)-dextran (Dex) has been studied. Mouse bone marrow-derived DC were generated by culturing the precursors with GM-CSF and subsequent exposure to TI-2 antigens in different concentrations. After the Dex pulse DC underwent activation, which was manifested as an increase of the number of CD80- and CD86-positive cells in the culture. Using flow cytometry, binding of FITC-labeled Dex by DC was established. At the FITC-Dex concentration of 80-100 mu g/ml, the number of DC that bound the antigen reached stationary level. To assess the immunogenic properties of DC charged by TI-2 antigens, the cells were mixed with normal mouse splenocytes and cultured in the complete RPMI 1640 medium for 4 days. The numbers of antibody- and immunoglobulin-forming cells (AFC and IFC, respectively) were determined by ELISPOT method. Cultures containing splenocytes and naive DC not pulsed by the antigens were used as control. An increase in the numbers of AFC and IFC under the influence of naive DC did not exceed 20%. In contrast, the addition of DC charged by the antigens increased a specific immune response more than 2.5-fold and an immune response induced by polyclonal antigens, by 40%. The data obtained provide the first indication of the direct interactions of DC with TI-2 antigens. Pulsed DC present TI-2 antigens to mouse splenocytes and induce specific and polyclonal B-cell activation.