TYPE-IV HYPERSENSITIVITY IN THE PATHOGENESIS OF FIPV-INDUCED LESIONS

In focal lesions of feline infectious peritonitis (FIP), the cells inv olved in the delayed-type hypersensitivity were identified in a formal in-fixed paraffin-embedded and frozen samples taken from 35 affected c ats. The clinical diagnosis of FIP was confirmed by necropsy, histolog y and direct immunofluorescence against the coronaviruses on cryostati c sections. The immune cells were detected immunohistochemically by th e Avidin-Biotin-Complex (ABC) method using either polyclonal antibodie s against lymphoid antigens (CD3) or monoclonal antibodies against lym phoid (PAN-T, CD4, CD8) and myeloid antigens (MAC387). Better identifi cation of T cells and macrophages were found on formalin-fixed paraffi n-embedded sections than on cryostatic ones, while T lymphocyte subpop ulations could be differentiated only in cryostatic sections. Type IV hypersensitivity was detected in focal feline infectious peritonitis v irus (FIPV)-induced lesions from progressive activation of T lymphocyt es, mainly CD4(+), and the presence of granulocytes and macrophages. T he FIPV-induced lesions could be studied as examples of granulomas cau sed by unconventional antigens, such as viruses or immune complexes.