Enhanced Antigen Presenting Cell Function Following in Vivo Priming

Abstract

The population of cells able to present antigen to class II MHC-restricted, CD4⁺ T helper cells appears heterogenous and, in the mouse, includes B lymphocytes, macrophages and DC. R. Steinman and collaborators¹ have shown that an antigen injected intravenously at high dose in a naive mouse was present in an immunogenic form on DC only, a finding that correlates with the unique capacity of the DC in stimulating antigen-specific, naive T cells. The cellular interactions leading to a specific immune response following the encounter with an antigen may be different in a primary and a secondary response. In particular, B lymphocytes which bind proteins to surface lg receptors have been shown to present these proteins at very low concentrations in vitro and in vivo ². Since antigen-specific B cells undergo clonal expansion, the B cells in a primed mouse represent a significant proportion among all antigen-presenting cells. Furthermore, circulating antigen-specific antibodies may form complexes with the antigen which can be taken up by FcR⁺ cells³. In this paper, we tested whether B cells and macrophages could play a role in antigen presentation in an anamnestic response in vivo, and compared the antigen presentation during a secondary versus a primary response.