Characterization of the diffuse mucosal associated lymphoid tissue of feline small intestine

Characterization of the feline intestinal mucosal associated lymphoid tissu e (MALT) will facilitate investigation of intestinal disease in the cat and promote the cat as an animal model for a range of human diseases which inv olve the intestinal lymphoid tissue. This includes inflammatory bowel disea se, viral and non-viral associated intestinal lymphomas and immunodeficienc y associated syndromes. Morphologic and phenotypic characterization of the normal small intestinal diffuse MALT in 22 SPF cats was performed using flo w cytometry and cytology on isolated intestinal leukocytes from the intra-e pithelial and lamina proprial compartments, as well as immunohistology on t issues from the feline duodenum, jejunum and ileum. The intra-epithelial co mpartment (IEC) was dominated by lymphocytes (>85%) which frequently contai ned intracytoplasmic granules. The most striking findings in the IEC were t he elevated percentages of CD8 alpha+ lymphocytes (40%), presumed to expres s CD8 alpha alpha chains, and CD4-/CD8- (double negative) lymphocytes (44%) , and the consistent presence of a minor subpopulation of CD3+/CD11d+ IELs (6%). Small percentages of CD4+ lymphocytes (10%) were observed such that t he ILL CD4:CD8 ratio (0.25) was low. The LPC also contained a majority of T cells rind few plasma cells. However, this compartment had reduced percent ages of CD8 alpha+ lymphocytes (28%) and increased percentages of CD4+ lymp hocytes (27%) relative to the IEC. However, the LPL CD4:CD8 ratio (1.0) rem ained low compared with the ratio in peripheral blood. In feline MALT, MHC class II expression was lower than in other peripheral lymphoid compartment s. The results of this study provide important reference values for future investigations involving feline intestinal lymphocytes and demonstrates tha t the leukocyte distribution and phenotypic characteristics of the feline d iffuse MALT appear largely similar to the murine, rat and human counterpart s. (C) 2000 Elsevier Science B.V. All rights reserved.