Attachment of mycoplasmas to erythrocytes: A model to study mycoplasma attachment to the epithelium of the host respiratory tract

Mycoplasma pneumoniae, M. gallisepticum and M. pulmonis are pathogens of the respiratory tract. Their adherence to the host tissue is a prerequisite for manifestation of the disease. The attachment occurs between membrane components of the mycoplasmas and the host cells. In the attachment of M. pneumoniae and M. gallisepticum, binding sites of a protein nature of the mycoplasma membranes interact primarily with sialic acid residues of sialoglycoproteins of the host cell membranes. The latter was clearly indicated in studies on the pathogenic strain of M. pneumoniae and its nonpathogenic nonhemadsorbing mutants, and by the assessment of the direct binding of glycophorin [the major sialoglycoprotein of human red blood cells (RBC)] and other sialoglycoproteins to M. pneumoniae and M. gallisepticum. The components involved in the interaction of M. pulmonis with the host cells are not as well characterized, since the attachment is not affected by proteolytic treatment of the mycoplasmas, nor by removal of sialic acid residues from the host cell membranes. The attachment of the mycoplasmas to the host cells also occurs with nonviable organisms and can, in addition, be reproduced by isolated membranes. The binding sites of M. pneumoniae and M. gallisepticum were partially purified by affinity chromatography, using the high affinity of the binding sites for glycophorin. By this procedure the membranes were solubilized with detergents and chromatographed through glycophorin attached to Sepharose 4B as an affinity matrix. The binding sites retained the high affinity for glycophorin and bound to RBC membranes. Are the binding sites distributed throughout the membrane? Since the binding of the mycoplasma is via a polar structure (the tip or bleb), one may suggest that these structures harbor them. Experimental evidence for their distribution is being sought.