The role of mycoplasma membrane proteins in the adsorption of animal cells to Mycoplasma hominis colonies.

Colonies of Mycoplasma pneumoniae and Mycoplasma gallisepticum adsorb many types of animal cell, including erythrocytes of various species, spermatozoa and tissue culture cells (Manchee & Taylor-Robinson, 1969). This adsorption can be prevented by treating the colonies with antiserum to whole mycoplasma organisms. The adsorption-inhibiting activity of the serum can in turn be abolished by treating the serum with haptens isolated from mycoplasmas. We have examined the role of specific mycoplasma antigens, particularly those of the cell membrane, in the adsorption of H-HeLa cells to colonies of a strain of Mycoplasma hominis. Mycoplasma horninis, sc4, isolated from the urethra of a man attending a venereal diseases clinic, was used throughout. Antisera to whole organisms, purified membranes and soluble fraction were those prepared by Hollingdale & Lemcke (1969). Antisera to lipid-free and recombined membranes and urea extract of whole membranes were prepared in rabbits according to Hollingdale & Lemcke (I 972). In the test for inhibition of H-HeLa cell adsorption, the culture medium, growth of mycoplasma colonies on agar and origin of H-HeLa cells were as described by Manchee & Taylor-Robinson (I 969). Suitable colonies of the mycoplasma, preferably in groups of three or four, were surrounded with a glazed porcelain assay cylinder; about six cylinders were used on each agar plate. Each cylinder was filled with a dilution of the antiserum, prepared by a twofold serial dilution in 20% (v/v) normal guinea-pig serum in phosphatebuffered saline pH 7-2. Control cylinders contained 20% (v/v) normal guinea-pig serum in phosphate-buffered saline alone. After the plates had been incubated at 37" for 3 h, the antiserum was replaced with H-HeLa cell suspension in phosphate-buffered saline (2 x 106 cells/ ml) and the plates reincubated at 37" for 2 h. The cylinders were emptied and removed, excess cell suspension removed with a few ml phosphate buffered saline and the colonies examined under a stereo-plate microscope. The adsorption-inhibition titre was taken as the reciprocal of the dilution of antiserum which reduced cell adsorption to 25 yo compared with untreated control colonies. The method for metabolic inhibition was as described by Hollingdale & Lemcke (1969). The metabolic inhibition titre was the highest dilution of antiserum inhibiting a colour change of 0.5 pH.