The role of complement in the acquired immune response.
Studies over the past three decades have clearly established a central role for complement in the promotion of a humoral immune response. The primary function of complement, in this regard, is to opsonize antigen or immune complexes for uptake by complement receptor type 2 (CR2, CD21) expressed on B cells, follicular dendritic cells (FDC) and some T cells. A variety of mechanisms appear to be involved in complement-mediated promotion of the humoral response. These include: enhancement of antigen (Ag) uptake and processing by both Ag-specific and non-specific B cells for presentation to specific T cells; the activation of a CD21/CD19 complex-mediated signalling pathway in B cells, which provides a stimulus synergistic to that induced by antigen interaction with the B-cell receptor (BCR); and promotion of the interaction between B cells and FDC, where C3d-bearing immune complexes participate in intercellular bridging. Finally, current studies suggest that CR2 may also play a role in the determination of B-cell tolerance towards self-antigens and thereby hold the key to the previously observed correlation between deficiencies of the early complement components and autoimmune disease.
Nielsen
C H
CH
Department of Immunology and Microbiology, University of Southern Denmark, Odense, Denmark.
Fischer
E M
EM
Leslie
R G
RG
D000917:Antibody Formation / Q000276:immunology*; D017951:Antigen Presentation / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology; D003165:Complement System Proteins / Q000276:immunology*; D020566:Dendritic Cells, Follicular / Q000276:immunology; D006801:Humans; D007108:Immune Tolerance; D008213:Lymphocyte Activation / Q000276:immunology
D003165:Complement System Proteins