Distribution of plaque-forming cells in the mouse for a protein antigen. Evidence for highly active parathymic lymph nodes following intraperitoneal injection of hen lysozyme.

The distribution of plaque-forming cells (PFC) throughout the lymphoid system of CBA mice was followed with time after a primary intraperitoneal injection of hen egg white lysozyme emulsified in Freund's complete adjuvant (HEL-CFA) and after a secondary soluble injection. Throughout the primary response (predominantly IgG) and during the first week of the secondary response (exclusively IgG), the highest density of PFC was found in the draining parathymic lymph nodes, followed by the local spleen and mesenteric lymph nodes. The antibody-forming activity of the bone marrow increased as the immune response progressed, so that by the 3rd week of the secondary response this compartment provided the majority of the PFC. PFC first appeared in the accessory axillary, brachial or inguinal lymph nodes and in the thymus a few days after the secondary injection but accounted for only 1-5% of the total activity during the entire course of the secondary response. The specificity of the antibody produced in the spleen, parathymic and mesenteric lymph nodes was identical as judged by plaque inhibition by seven chemically related lysozymes which implies that these PFC were well mixed. It is postulated, therefore, that the change in distribution of PFC from an early local response to a general systemic response, and finally to a predominantly bone marrow response, was due to the migration of memory cells from the draining parathymic lymph nodes and spleen throughout the lymphoid system with an ultimate settling of the cells in the bone marrow.