Further characterization of human myeloid antigens (gp160,95; gp150; gp67): investigation of epitopic heterogeneity and non‐haemopoietic distribution using panels of monoclonal antibodies belonging to CD‐11b, CD‐13 and CD‐33

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Abstract
Summary. We have investigated the binding of over 30 different monoclonal antibodies (MAB) belonging to three distinct clusters of differentiation (CD-11b; CD-13; CD-33; as defined by the Third International Workshop on Leucocyte Differentiation Antigens (ILWS), 1986), and which are reactive with three distinct myeloid restricted surface antigens (‘gp160,95′; ‘gp150′; ‘gp67′). By investigating reactivity with non-haemopoietic cells, we have confirmed that CD-11b and CD-33 MAB reactivity is largely restricted to haemopoietic cells, whilst CD-13 MAB showed additional binding to a wide range of non-haemopoietic cells. Epitopic heterogeneity was also investigated within each cluster of differentiation. Tested anti-CR3 (CD-11b) MAB varied in their ability to block the binding of complement coated sheep red blood cells and zymosan particles. A more detailed analysis of MAB binding heterogeneity was performed by competitive inhibition assays. It was demonstrated that MAB from both CD-11b and CD-13 bind to several distinct epitopes (at least six and five respectively) on their respective antigen molecules. In contrast, CD-33 MAB appear to bind to only a single site on ‘gp67′. These data may allow for a clearer appreciation of the disparate functional effects obtained using different MAB reagents to individual myeloid antigens, as reported by a number of workers.