Migration of newly formed small lymphocytes from bone marrow to lymph nodes during primary immune responses.

Selective DNA labelling of bone marrow cells was used to determine the effect of antigenic stimulation on the migration of small lymphocytes from bone marrow to popliteal lymph nodes. Following footpad injection of keyhole limpet haemocyanin (KLH) in guinea-pigs the regional nodes showed an early increase in weight and cellularity together with a progressive increase in cell proliferation. When [H]thymidine was injected into tibial and femoral marrow 2 days before KLH administration the DNA radioactivity of the KLH-stimulated nodes increased rapidly and always exceeded that of contralateral nodes. Simultaneously, in radioautographic sections of lymph nodes labelled small lymphocytes, indicative of an origin from marrow precursors, appeared throughout the cortex, post-capillary venules, subcapsular sinus, medullary cords and sinuses. In KLH-stimulated nodes the number of labelled small lymphocytes per section was higher than in contralateral nodes, especially in the cortex, and some of these cells appeared in germinal centres. Labelled large blast cells and macrophages were also increased in numbers. Similar changes were observed in lymph nodes of parental strain rats following intramyeloid [H]thymidine administration and footpad injection of lymphoid cells from F1 hybrid rats. The results demonstrate that, during the early response of lymph nodes to various antigens, local changes in cell traffic include an enhanced accumulation of newly formed small lymphocytes, putative virgin B lymphocytes, generated in the bone marrow prior to the antigenic stimulation.