MUCOSAL MEMORY B-CELLS RETAIN THE ABILITY TO PRODUCE IGM ANTIBODIES 2YEARS AFTER ORAL IMMUNIZATION

In recent studies we have demonstrated that immunological B- and T-cel l memory may be stimulated effectively by oral immunization, simply by admiring protein antigens with cholera toxin (CT) adjuvant. Here we e xtend the information by employing a hapten-carrier system allowing us to separate B- and T-cell memory and to evaluate the requirement of m emory T cells for effective reactivation of mucosal memory B cells. We found that 2 weeks following oral priming immunizations with dinitrop henyl-keyhole limpet haemocyanin (DNP-KLH) plus CT adjuvant, significa nt serum anti-DNP antibodies of IgG, IgA and IgM immunoglobulin classe s were demonstrated. However, after 2 years only IgM anti-DNP antibodi es could still be detected in serum. When memory lymphocytes were isol ated from these mice, from both systemic and gut-associated lymphoid t issues, and challenged with antigen in vitro, vigorous IgM, but no IgG or IgA, anti-DNP production was observed. By contrast, when the DNP-K LH-primed memory mice were challenged in vivo by an oral booster immun ization with DNP-KLH plus CT adjuvant, strong systemic IgG and local m ucosal IgA anti-DNP responses were recorded, while IgM anti-DNP produc tion was poor. Moreover, the mucosal memory B cells from DNP-KLH-immun ized mice were more responsive in vivo to an oral booster immunization with the carrier-specific antigen, DNP-KLH, compared to that provided by an unrelated carrier, DNP-human serum albumin (HSA), which gave on ly poor mucosal and systemic anti-DNP B-cell responses. Taken together our data suggest that mucosal memory B cells are recirculating cells that have retained their ability to produce IgM antibodies and, theref ore, have not undergone switch differentiation involving gene rearrang ements with constant mu-chain deletions. Furthermore, mucosal B-cell m emory and CD4(+) T-cell memory are closely interconnected phenomena, r equiring both components for effective expression and probably also fo r maintenance of immunological memory in the mucosal immune system.