Isolation and characterization of the soluble and membrane-bound porcine CD44 molecules

Porcine CD44 was identified by the cross-reactive anti-human CD44 monoclonal antibody (mAb) Hermes-1. Material which inhibited the Hermes-1 mAb binding to porcine lymphocytes was found in porcine intestinal efferent lymph and demonstrated to be a soluble form of porcine CD44. A protocol using non-affinity techniques was established to isolate this material from porcine lymph. The isolated soluble CD44 molecule consists of a single peptide with an apparent MW of about 50,000, containing the Hermes-1 epitope. The soluble and membrane-bound forms of porcine CD44 were also affinity purified and characterized. The soluble CD44 preparation comprised a major component of 48,000-70,000 MW peptide and a minor band of 120,000 MW. The membrane-bound CD44 preparation contained a 90,000 MW major and a 120,000 MW minor component. Both the major components of the soluble and membrane-bound forms of porcine CD44 contained N-linked glycosylation. The 48,000-70,000 MW component of the soluble CD44 molecules consisted of two subsets discriminated by their binding capacity for lentil lectin and a slight difference in molecular weights. Soluble CD44 molecules were also identified in the sera of sheep, goats, horses, dogs and humans. Like the porcine counterpart, these molecules could be enriched by anion-exchange chromatography, suggesting that they have similar biochemical properties.