Virgin B cell recruitment and the lifespan of memory clones during antibody responses to 2,4-dinitrophenyl-hemocyanin.

The extent to which B cells newly formed in the bone marrow contribute to primary and secondary B cell responses was investigated. This was assessed by constructing chimeras between congenic strains of rats differing in their kappa light chain allotype. Recipient animals received 800 cGy whole body irradiation with hind limb shielding to protect a proportion of their hemopoietic capacity. These rats then received 3 X 10(8) kappa allotype-marked thoracic duct lymphocytes from donors previously immunized twice with either dinitrophenylated spider crab (Maia squinada) hemocyanin (DNP-MSH) or MSH alone. The chimeras were immunized with DNP-MSH and the production of anti-DNP antibody of both donor and host origin was measured. In the period immediately after immunization both newly formed host virgin B cells and donor memory B cells gave rise to substantial proportions of the anti-DNP antibody. After this initial period, antibody production became sustained by activation of memory B cells only. The chimeras were reimmunized with DNP-MSH at 32 days after their first immunization. There was again evidence of a brief period of both virgin and memory B cell activation followed by memory B cell activation only. Donor B cell clones remained dominant in the established response throughout the 5 months each chimera was studied. The data are interpreted as indicating two phases of B cell activation. It is suggested that the first phase where both virgin and memory B cells are activated may be associated with antigen presentation on dendritic or interdigitating cells outside follicles. It is argued that the second phase where only memory B cells are activated is more likely to be associated with antigen on follicular dendritic cells.