Identification of three myeloid-specific differentiation antigens in sheep

The monoclonal antibodies submitted to the Third Workshop on Ruminant Leukocyte Antigens were analysed for their reactivity with sheep macrophage and monocyte populations. Initial analysis showed that, in addition to the anti-integrin mAbs, there were six mAbs that reacted with macrophages or monocytes but were unreactive on lymphocytes. Preliminary flow cytometry and immunohistology showed that there were three distinct groups of mAbs: Group 1 consisted of VPM65, VPM66 and VPM67; Group 2 consisted of just VPM64; Group 3 consisted of just VPM63. Further analysis demonstrated that Group 1 mAbs recognize the sheep homologue of CD14. Group 2 reacts reacts with an Mr 65 000–80 000 polypeptide possibly analogous to CD16 (FcγRIII) and Group 3 reacts with an Mr 40 000–42 000 doublet, probably identified as a minor isoform of sheep FcγRII (CDw32). Another mAb (IL-A97) was similar in many respects to the Group 1 mAbs but there was a lack of data to confirm its specificity. All mAbs tested also reacted with cattle macrophages.