Dynamics of cell populations in lymph node during primary immune response.

Abstract

Based on the concept that the lymph node is composed of four functionally distinct compartments, popliteal lymph nodes of three week-old rats were studied histologically after a single primary antigenic stimulation. A variety of antigens, i.e., SRBC, pertussis vaccine, bovine r-globulin, crystalline bacterial amylase, egg albumin, diphtheria toxoid with or without the adjuvant always producerl. a con· sistent pattern of development and involution sequentially in each of four com­ partments: the paracortical areas were always the first in making response, fol­ lowed primary follicles, medullary cords and germinal centers in this order. The mitotic indices in the paracortical areas reached the maximum on the third day whereas the peak activity of the germinal center s was observed between the lOth to 24th day. The development of germinal centers which had not been observed until the late stage might reflect its probable role in the development of immunological memory. The role of paracortical areas in the initiation of "true" primary re­ sponse was discussed in the light of current theories on the cell-to-cell interaction as well as the relationship between humoral and cell-mediated immune response. This led to postulation that the par acortical hyperplasia was essential for the induction of primary immune response, especially in "true" primary respons e.