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Immunoglobulin (Ig) isotype switching and commitment, generation of memory cells, and the functional potential of B cell subsets have been analyzed in two different clonal microcultures. One is antigen (Ag)-dependent, haplotype-restricted, and requires linked recognition of hapten and carrier. The other is Ag-independent and relies on the stimulation of single I-Ab cells by alloreactive D10 helper T cells. Immunising mice increased the frequency of clonal precursors among hapten-gelatin enriched cells as well as the proportion of clones secreting non-IgM isotypes. IgA was produced when either purified dendritic cells (DC) or IL-5/IL-6 were added to the T-B cultures. sIgD+ cells could be induced to produce a wide range of isotypes including IgA whereas a majority of sIgA+ cells produced IgA exclusively. Germinal centre (GC) cells could be stimulated in both systems to divide and produce antibody and this subset appears to contain a radiation-resistant population that secretes mainly IgA upon allo -recognition by D10 cells in the presence of DC.

We have developed a number of in vivo and in vitro systems for testing the functional potential of gut T- and B- cells primed in vivo via acute or chronic stimulation of the intestinal mucosa with reovirus or Morganella morganii (M.m.) respectively. Reovirus type 3 given orally to neonatal, normal mice or adult severe, combined immunodeficient (scid) mice results in a disseminated fatal infection due to meningoencephalitis at 10–12 d in the pups and to focal hepatitis and liver failure at 4–6 wk. in the scid mice. IELs (106) from adult, immune mice given to pups challenged one d later can prevent development of brain lesions. The protective effect of IELs is decreased after treatment with anti-Thy1 + C’ and eliminated after treatment with anti-CD8 + C’. Transferred Peyer’s patch (PP) cells from immune, congenic normal donors can likewise prevent dissemination of viral infection in scid mice challenged 2 d later. The most effective subset of PP cells is Thy1+, CD8+, and GCT+.