Secondary antibody responses to thymus-independent antigens. Decline and life-span of memory

Immunological memory has been defined by the finding that upon a secondary injection of an antigen into an animal the immune response obtained differs from the response produced after the first inoculation of the antigen, independent of the length of time that can elapse between the first and second contact with antigen. In this report we have investigated the life-span of memory to a thymus-independent antigen, trinitrophenylated lipopolysaccharide (TNP-LPS), using a cell transfer system that allows the study of the function of isolated LPS-reactive "memory" B cells from C57BL/6 mice in histocompatible LPS-nonresponder C57BL/10ScCr hosts. We found that the longer the elapse of time between the transfer of TNP-LPS-primed C57BL/6 cells and the challenge of hosts with TNP-LPS, the lower the anti-TNP serum antibody level of the secondary response, i.e. in the absence of antigen, TNP-LPS memory cells have a short life-expectancy in the adoptive hosts as they do not persist for more than one or two weeks after transfer. Our present results suggest that induction and long-term persistence of memory to TNP-LPS in adoptive hosts cannot be solely explained by the long life-span of a subpopulation of antigen-specific memory B cells, but rather through the continuous recruitment of newly formed cells and probably antigen persistence.