A substantially pure, covalently linked human T cell reactive feline protein (TRFP) has been isolated from vacuum bag extract obtained by affinity purification of house dust collected from several homes with cats; DNA encoding all or a portion of the TRFP or peptide; compositions containing such a protein or peptide or portions thereof; and antibodies reactive with the TRFP or peptide are disclosed. Also disclosed are recombinant TRFP or peptide; modified or mutated TRFP peptides; their use for diagnostic or therapeutic purposes.