The role of T cells and adjuvant in the immune response of mice to foreign erythrocytes

The splenic response of CBA mice, deprived of thymus‐derived cells (T cells), to the injection of different doses of sheep erythrocytes, has been compared to that obtained in control mice which possess T cells. The effect of pertussis injected with the antigen was measured in both groups of mice in terms of the number of plaque‐forming cells (PFC) to sheep red blood cells (SRBC) of the five main immunoglobulin classes of mice. The following conclusions have been reached: Increasing the antigen concentration does not overcome the depression in the immune response resulting from an absence of T cells; consequently this evidence is incompatible with the role of T cells being solely one of concentration of antigen to B cells. As the antigen dose is increased, the direct effect of adjuvant on B cells is also increased, whereas it is argued that an inverse relationship exists for the effect of adjuvant on T cells in the antigen dose range used here. The lower the concentration of antigen, the greater is the dependence of the adjuvant effect of pertussis on the presence of T cells. This is far apparent for γM‐PFC than for non‐γM‐PFC. A significant proportion of γM‐PFC are produced from precursor cells, which do not appear to require T cells for their differentiation into antibodyforming cells. It is possible that adjuvant and T cells stimulate B cells in a similar way. Previously published evidence, which was thought to support the antigen‐concentration hypothesis of T cell action, may have been an artefact due to the direct action of adjuvant (or adjuvant‐like properties of the antigen preparation itself) on B cells binding antigen. An effect consisting of an impaired γG l response is described in fetal liver reconstituted and one‐year old normal mice. The effect is independent of irradiation received during reconstitution and may be due to a partial deficiency of T cells in old age.