Immunohistochemical characterization of hepatic lesions associated with migrating larvae of Ascaris suum in pigs.

This paper describes the histopathological features and the cellular distribution of T lymphocytes (CD3), B cells (CD79a), immunoglobulin (IgG, IgA, IgM)-bearing plasma cells, macrophages (Mac387 and alpha-1-antitrypsin), MHC class II antigen and S-100 protein in hepatic white spots associated with naturally occurring Ascaris suum parasitism in 35 pigs. Hepatic granulomas were observed in 10 pigs, whereas lymphoid proliferation with a diffuse or lymphonodular pattern was the main histopathological lesion in 14 other pigs, and portal fibrosis in a further 11 animals. In lymphonodular lesions, the distribution of immunoreactive cells with all antibodies tested was closely similar to that found in the cortex of lymph nodes. Thus, lymphoid follicles were composed mainly of CD79a(+)B cells and interfollicular tissue was composed mainly of CD3(+)T lymphocytes. The presence of follicular dendritic and interdigitating cells expressing S-100 protein and MHC class II antigen in lymphonodular lesions suggested that these are highly organized structures developed to enhance antigen presentation to B and T cells, and consequently the local immune response against the parasite. The humoral local response was represented mainly by IgG-secreting plasma cells.