Canine leukocyte integrins: characterization of a CD18 homologue.

The major characteristics of the canine CD18 leukocyte antigen family, defined by a murine monoclonal antibody CA1,4E9, are described. The overall molecular organization of this family of leukocyte integrins was similar to the human counterpart, and consisted of a common beta subunit of 95 kD (CD18) and non-covalently linked alpha subunits of 150 kD (CD11C), 165 kD (CD11b) and 180 kD (Cd11a). Conservation of CD18 epitopes between dog, human, feline, equine and bovine was observed. CD18 expression in lymphoid tissue had a characteristic pattern which was based on differences in the intensity of expression observed in different cell types. The expression of LeuCAMs in canine epidermotropic lymphosarcoma (mycosis fungoides) was also explored since LeuCAMs might be expected to play a major role in the tissue tropism of this tumor. Intense CD18 expression was observed in the malignant T cells which infiltrated the epidermis; these cells differed phenotypically from dermal T cells in that they often lacked Thy-1 expression. The potential pathogenetic significance of LeuCAM expression in canine mycosis fungoides is discussed.