Prolonged administration of antithymocyte serum in mice. II. Histopathological investigation.

Prolonged administration of ATS to mice resulted in depletion of small lymphocytes in the thymus-dependent (paracortical) areas of lymph nodes in all mice. Small lymphocyte depletion of the thymus-dependent periarteriolar region of the spleen was present in most mice, although this feature was masked by plasmacytosis in this region in some. Depletion of small lymphocytes in the thymus-dependent areas of Peyer's patches was evident in some of the younger mice. None of these changes in lymphoid organs were seen in control mice, untreated or given NRS. The thymus was unaffected except in some ATS- or NRS-treated mice which were sick and/or old, in which the narrowing of the thymic cortex was attributed to non-specific stress. Plasmacytosis was seen in the medullae of lymph nodes of both ATS- and NRS-treated mice, although it was more intense in the latter. In non-lymphoid organs the most striking changes were seen in the kidneys of mice treated both with ATS and NRS. Complex-type nephritis followed by amyloidosis was seen in a large proportion of mice over 6 months old in both these groups and in these mice amyloid was seen frequently in other organs, including spleen and liver. Tumours occurred in fifty-four ATS-treated mice, but in no other group. Fifty-two of these tumours were attributable to polyoma virus; two other were lymphoblastomas. Reticulum cell hyperplasia was seen in two further mice.