A comparative study of the microcirculation in the guinea-pig thymus, lymph nodes and Peyer's patches.

The circulatory patterns in three lymphoid tissues were compared macro- and microscopically. Indian ink or a viscous silicone rubber compound were used as contrast materials and serial 75 micronm sections examined. The findings were checked with the benzidine stain for red blood corpuscles in uninjected tissues. Thymic lobules showed a "through circulation"--capillaries penetrating the cortex from within outwards and draining into surface veins, comparable with the circulation in liver lobules. By contrast, lymph nodes and Peyer's patches showed a looped capillary distribution. The outer thymic cortex and primary follicles in lymph nodes contained the maximum capillary density, correlating with the highest mitotic index of thymocytes and lymphocytes in the respective tissues. The lowest vascular density in the thymus was in the medulla, particularly in Hassall's corpuscles, in secondary follicles of lympho nodes and Peyer's patches, which correlates with the storage capacity of antigens and antibodies at those sites. Postcapillary venules in lymph nodes and Peyer's patches showed a characteristic pattern with Indian ink. These venules were absent from the thymus.