Differences between virgin and memory IgM-antibody-forming-cell precursor B-cells, and correlations with the heterogeneity present in B-cell populations from unimmunized mice

Histophysiology of follicular structures and germinal centres in relation to B cell differentiation

A historical review of germinal centres since their original description in 1885 by Flemming is given, followed by a description of the germinal centre reaction. Microenvironmental aspects are discussed, special attention being paid to the role of antigen in the induction and further regulation of germinal centre activity. Germinal centres give rise to a new population of lymphocytes (germinal centre-derived cells). Their immune capacities were studied using the rabbit appendix as an experimental model. The possible properties of the cell from which a germinal centre develops (germinal centre precursor cell) were investigated using germinal centre cell suspensions from the rabbit appendix and bone marrow and thoracic duct lymphocytes in the rat in adoptive transfer systems. From these experiments a working hypothesis was formulated for the possible role of germinal centres in B cell differentiation. Essentially, germinal centres are thought not only to be sites of selective amplification of antigen-reactive but still immature B cells, resulting in the generation of memory cells, but also to contribute to the overall pool of B cells by polyclonal amplification of B cells of specificities unrelated to the antigen inducing the germinal centre.

Optimal strategies in immunology. II. B memory cell production

After a first encounter with most antigens, the immune system responds to susequent encounters with a faster, more efficient and more strenuous antibody response. The memory of previous antigen contacts is carried by lymphocytes. Expanding on the model developed in Part 1 of this paper, we examine the optimal strategy available to the immune system for B memory cell production. We again find that the strategy should be of the bang-bang variety. The model we consider assumes that antigen triggers a subpopulation of B-lymphocytes. These triggered lymphocytes can proliferate and secrete modest amounts of antibody, or differentiate into non-dividing plasma cells which secrete large amounts of antibody, or differentiate into non-antibody secreting memory cells. Given injections of antigen at two widely spaced times we compute the strategy which minimizes a linear combination of the primary and secondary response times. We find that for all biologically reasonable parameter values the best strategies are ones in which memory cells are produced at the end of the primary response. Exerimental results which bear on the actual strategies employed are discussed.