ANTIBODY-RESPONSE TO A T-DEPENDENT ANTIGEN REQUIRES B-CELL EXPRESSIONOF COMPLEMENT RECEPTORS

Several Lines of evidence indicate that antibody responses to T-depend ent antigens require complement receptors expressed on either B lympho cytes or follicular dendritic cells. We have used RAG-2-deficient blas tocyst complementation to create mice specifically lacking B cell comp lement receptors. Despite normal expression of complement receptor 1 ( CR1 [CD35]) and CR2 (CD21) on follicular dendritic cells, these mice h ave a profound defect in their capacity to mount a T-dependent antibod y response. This is the first direct demonstration in vivo that B cell expression of complement receptors is required for a humoral immune r esponse. This suggests that CD21 and/or CD35 on B lymphocytes may be r equired for cellular activation, adsorptive endocytosis of antigen, re cruitment to germinal centers, and/or protection from apoptosis during the humoral response to T-dependent antigens.