Attachment of mycoplasmas to host cell membranes

Pathogenic mycoplasmas rarely invade the tissues or bloodstream. Their adherence to epithelial cell surface, the first stage in disease, involves protein binding sites on the mycoplasmal cell membrane and receptors on the host cell membrane. Strong evidence indicates that Mycoplasma gallisepticum and Mycoplasma pneumoniae adhere with the aid of sialic acid residues on host cells, but the data do not preclude participation by other host-cell membrane components. Several studies indicate that these mycoplasmas adhere by blebs or terminal structures; others suggest that binding occurs via other cell areas. Scanning electron microscopy suggests tight interaction between these mycoplasmas and red blood cell membranes, causing imprints resembling those from interaction of viruses with red blood cells. Because sialoglycoproteins are major sites for attachment of M. pneumoniae to respiratory epithelium and red blood cells, glycophorin--the major sialoglycoprotein of human red blood cells--was the ligand used in affinity chromatography for isolation of the binding sites specific for sialic acid receptors from M. pneumoniae membranes solubilized by detergents. The fraction eluted with 0.2% sodium dodecylsulfate from the glycophorin-Sepharose column, highly enriched with two proteins, exhibited high binding capacity to glycophorin-Sepharose beads and lower binding capacity to human red blood cells. The latter capacity was nearly abolished by glycophorin, but not by its hydrophobic moiety.