Compositions enriched for Neutrophil Inhibitory Factor which inhibit neutrophil activity including adhesion to vascular endothelial cells are provided. Also provided are recombinant Neutrophil Inhibitory Factors which also which inhibit neutrophil activity. Such compositions may comprise a glycoprotein isolated from nematodes. These compositions and recombinant Neutrophil Inhibitory Factors are useful in the therapy of conditions which involve abnormal or undesired inflammatory responses.