Site of initiation of the plasma cell reaction in the rabbit lymph node. Ultrastructural evidence for two distinct antibody forming cell precursors.

Two times sublethal total body-X-irradiation with weekly local thymus irradiation established a T-cell deprived experimental model in rabbits. Humoral immunity reactions in draining lymph nodes have been analyzed histologically and at the submicroscopical level after challenge with Salmonella Java vaccine, horse spleen ferritin, horse-gamma-globulin, a chemical sensitizer oxazolone (2 phenyl-4-ethoxymethylene-5-oxazolone) and after skin allografting respectively. The time sequence studies in these animals with an 'isolated B-cell system' are compared with similar experiments in normal non-irradiated rabbits. The site of initiation of the thymus-independent and thymus-dependent plasma cell response is established in the lymph node. The (ultra)structural features of the antibody forming (-B-)cell precursors, the marginal zone cells, are described and discussed. The differentiating off-spring of two (sub)microscopically recognizable plasma cell lines is presented.