RABBIT INTERLEUKIN-1 RECEPTOR ANTAGONIST - CLONING, EXPRESSION, FUNCTIONAL-CHARACTERIZATION, AND REGULATION DURING INTESTINAL INFLAMMATION

Genomic and cDNA clones for rabbit interleukin-l re antagonist (IL-1ra ) were isolated based on homology with the human, mouse, and rat IL-1r a gene. A partial genomic clone, obtained by screening a rabbit genomi c library, contained coding sequences for the carboxyl-terminal 108 am ino acids of rabbit IL-1ra. Two classes of cDNA for rabbit IL-1ra were obtained using RNA from inflamed rabbit colon tissue. One class of cD NA coded for a secreted form of IL-1ra, whereas the other coded for a putative intracellular form of rabbit IL-1ra. The latter form is simil ar to that isolated from human epithelial cells. A partially synthetic rabbit IL-1ra gene was constructed and expressed in Escherichia coli. The recombinant rabbit IL-1ra was purified to ho mogeneity by ion exc hange chromatography. Its affinity was similar to that of human IL-1ra for the human and mouse type I IL-1 receptor. From the cDNA clone and the purified recombinant protein, specific probes were developed for measuring levels of rabbit IL-1ra mRNA and protein in normal and infla med rabbit tissues. Unlike IL-1 alpha and IL-1 beta, IL-1ra mRNA and p rotein were present at detectable levels in normal rabbit colon. Durin g the development of an experimental formalin-immune complex colitis, rabbit IL-1 alpha showed a dramatic increase in tissue levels, consist ent with previous results; IL-1ra also increased 3-4-fold. Treatment o f colitis rabbits with corticosteroids significantly suppressed neutro phil infiltration, IL-1 alpha levels, but not IL-1ra levels. In contra st, corticosteroid treatment suppressed IL-1ra but not IL-1 alpha mRNA steady-state levels. Our observations demonstrate that IL-1 and IL-1r a synthesis is differentially regulated in healthy and inflamed intest inal tissue.