These results suggest that the anatomical distribution of VF differs between children and adults, perhaps relating to the different shape of the immature spine, notably the changing ratio of kyphosis to lordosis.

The antibody responses of mouse spleen cells in vitro to three thymus-independent (TI) antigens namely, polymeric flagellin (POL) of Salmonella adelaide, DNP-Ficoll and "soluble" sheep erythrocyte (SRBC) antigen, were found to be dependent on adherent accessory cells (A cells) but to a lesser degree than the response to intact SRBC. Evidence for this comes from selective depletion of A cells from spleen cells and reconstitution with A cell-rich populations. Thus, depletion of A cells by adherence on glass resulted in abolition of the response to SRBC leaving the response to POL intact. More thorough removal of A cells by treatment with carbonyl iron powder was required for appreciable reduction of the responses to POL, DNP-Ficoll and "soluble" SRBC. This reduction in responsiveness was not due to poor cell survival after A cell depletion or to the loss of immunocompetent cells since 1) the recoveries of viable cells in all cultures were similar; 2) the contents of theta- and Ig-bearing cells and tritium-labeled POL-binding cells were unaltered after carbonyl iron treatment, and 3) responsiveness was fully restored by the addition of irradiated and anti-theta-treated A cells from the peritoneal cavity or the spleen. Hence, the hitherto A cell independence of TI antigens on which some theories of B cell activation are based is a result of inadequate depletion procedures, and the minimal model for B cell activation must take into account two cell types: B cells and A cells.

Concanavalin A (Con A) has been shown t o act differently on bone marrowderived (B) cell responses to antigen in vitro, depending on the presence or absence of thymus-derived (T) cells. When T cells were present, Con A s u p pressed the immune response t o polymeric flagellin (POL) of SalmoneZla adelaide (a Tindependent antigen) and sheep erythrocytes (SRBC) (a T-dependent antigen). In contrast, when T cells were absent, Con A enhanced the anti-POL response and allowed an otherwise very low anti-SRBC response to return to normal levels. Con A inhibited POL-induced capping in a manner that was apparently independent of the presence of T cells. In a number of cases, the effects noted with Con A were also found with another mitogen, phytohemagglutinin. Some possible implications of these findings on the mechanism of T-B cell collaboration and the relationship between capping and immune induction are discussed.

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