INTERLEUKIN-5 MESSENGER-RNA EXPRESSED BY EOSINOPHILS AND GAMMA DELTA T-CELLS IN PARASITE-IMMUNE SHEEP/

Interleukin (IL)-5 is produced by a variety of cell types and contribu tes to both lymphocyte development and eosinophil terminal differentia tion in vitro. The coincidence of worm expulsion and eosinophilia in s heep infected with the gastrointestinal nematode Trichostrongylus colu briformis suggests that eosinophils may be involved as effector cells in host immunity against parasite infection. The role of IL-5 in this process was investigated by observing the distribution of IL-5 mRNA(+) cells in the small intestine, mesenteric lymph nodes (MLN) and Peyer` s parches (PP) by an in situ hybridization technique using a murine IL -5 riboprobe. IL-5 mRNA(+) cells were distributed throughout the lamin a propria (LP) of the small intestine from the tips of the villi to th e muscularis mucosae and in the parafollicular areas of MLN and PP in both naive and immune sheep. The phenotypes of IL-5 mRNA(+) cells was explored by simultaneous eosin and immunohistochemical staining using a monoclonal antibody recognizing the T19 marker. which identifies a m ajor subset of gamma/delta TCR(-) cells in sheep. In immune sheep. the re was about a five-fold increase in the number of eosinophils and IL- 5 mRNA(-) cells in the LP, but there was no significant change in numb ers of T19(-) cells. Most of the IL-5 mRNA(-) cells in the LP were eos inophils, but many of the T19 cells also expressed IL-5 mRNA. In contr ast, there were fewer eosinophils than T19(-) cells in MLN of immune s heep and, compared to controls, a three-fold increase in T19(+) cells and a five-fold increase in T19(-)/IL-5 mRNA(-) double-positive cells was observed in immune sheep. In PP, there were very few eosinophils b ut substantial numbers of T19(+) cells; however, no significant differ ences in numbers of eosinophils, T19(+) or IL-5 mRNA(-) cells were obs erved between control and immune sheep. These results indicate that in sheep, both eosinophils and gamma/delta T cells are capable of IL-5 e xpression and suggest that IL-5 is an important regulatory factor in a utocrine and paracrine activation of effector cells involved in parasi te immune expulsion.