Studies with Brugia pahangi. III: Histological changes in the affected lymph nodes of infected cats.

Cats infected with Brugia pahangi by single or repeated inoculation of infective larvae for different periods of time, were autopsied and the affected lymph nodes examined histologically, stained with methyl green and pyronin Y, haematoxylin and eosin, Lendrum's eosinophil stain, Mallory's trichrome stain or the May-Grunwald Giemsa technique. In single infections, there was initially a cell-mediated type immunological response which was characterized by proliferation of mononuclear thymus-dependent cells in the paracortical region of the lymph node. The antibody-type response became more evident as the infections progressed. This response was characterized by proliferation of lymphocytes in rapidly enlarging germinal centres and the production of large numbers of plasma cells in the cortico-medullary junction and medullary cords of the nodes. In long term infections, the affected afferent lymphatic vessel and popliteal node were almost obliterated by fibrous tissue, but an inguinal lymph node complex usually developed to replace lymphatic filtration in the limb. Repeated infections produced more complicated changes. Both types of response occurred to varying degrees throughout the infection. No significant increase in mast cells or eosinophil cells was seen. Fibrous tissue increased in the lymph nodes only after long periods of infection; such nodes often became non-functional, and by-passed by new lymphatic vessels.