Isolation of an immunosuppressive trauma peptide and its relationship to fibronectin

The purpose of this study was to characterize a suppressive active glycopeptide (SAP) using affinity chromatography (AFFI) and explore its similarity to fibronectin (FN) degradation products. It is postulated that SAP is a degradation fragment of a large serum-borne protein, possibly FN. Human trauma serum (HTS) and elastase-degraded human FN were run over an AFFI prepared with monoclonal antibody to SAP. Bound protein was eluted with 2M NaCl and dialyzed to remove salt. Immunosuppressive activity of HTS and FN eluates was monitored using inhibition of neutrophil chemotaxis (CTX). Active fractions were compared to the starting material and controls with 15% PAGE. AFFI eluates of HTS revealed a high molecular weight protein band (450 kd) with no inhibitory CTX activity and singular low molecular weight protein (LMW) band (less than 20,000) with 93% +/- 5% CTX suppression. Elastase-digested purified human FN eluates run under identical conditions over the same AFFI revealed two bands with an identical elution profile as HTS eluates. CTX suppression 95 +/- 5% was seen only with the LMW band. Incubation of enriched LWF fragments of digested FN and HTS with whole FN reversed CTX suppression. This suggests affinity purification of a single LMW suppressive glycopeptide which may bind to or be a degradation product of plasma or cellular fibronectin.