DIFFERENCES IN E-SELECTIN EXPRESSION AND LEUKOCYTE INFILTRATION INDUCED BY INFLAMMATORY AGENTS IN A NOVEL SUBCUTANEOUS SPONGE MATRIX MODEL

We have developed a novel subcutaneous sponge matrix model in major hi stocompatibility complex (MHC) homozygous SLAb/b inbred pigs to study lymphocyte-endothelial cell interactions during inflammation. Polyethe r sponges were implanted subcutaneously and left for 12 days before in jection of proinflammatory agonists. Implanted sponges became highly v ascularized and showed markedly increased uptake of i.v.-injected Cr-5 1-labelled lymphocytes 5 hr after injection of tumour necrosis factor- alpha (TNF-alpha) (3000 U) or phytohaemagglutinin (PHA) (37 mu g). Low er levels of traffic were seen in sponges 5 hr after injection with in terleukin-1 alpha (IL-1 alpha) (3000 U) and no significant traffic occ urred in sponges injected with phorbol 12-myristate 13-acetate (PMA) ( 15 ng) at 5 hr or PHA at 24 hr (compared to sponges injected with medi um alone). Electron microscopy of control sponges revealed low numbers of infiltrating leucocytes and relatively 'flat' endothelium. Many mo re infiltrating leucocytes were present in PHA-injected sponges. Howev er, no ultrastructural evidence was seen of any significant difference between control and activated endothelium. Immunocytochemistry of fro zen sections from sponges showed that E-selectin expression was up-reg ulated markedly by TNF-alpha and PHA at 5 hr, only moderately by IL-1 alpha at 5 hr, and not at all by PMA at 5 hr. By 24 hr in PHA-injected sponges E-selectin expression had fallen markedly from the level seen at 5 hr. Flow cytometric analysis of cellular infiltrates dispersed f rom sponges injected with TNF-alpha, PHA, IL-1 alpha or medium alone, revealed differences in lymphocyte subset populations. The infiltrate in sponges injected with TNF-alpha 5 hr before removal was dominated b y high numbers of CD2(+) lymphocytes, whereas the infiltrate induced b y PHA showed relatively higher levels of CD2(-) CD4(-) CD8(-) gamma de lta T-cell receptor(+) (TCR(+)) T cells revealed by population-specifi c monoclonal antibodies (mAb). This model, which permits harvesting of leucocytes and endothelial cells for manipulation in vitro, will be u seful for the study of leucocyte-endothelial cell interactions in suba cute and chronic inflammation.