RECENTLY, a complement-dependent, mycoplasmacidal reaction was described involving T-mycoplasmas and specific antibody (Lin and Kass, 1970). The concentration of urea in the medium was found to be critical for the demonstration of this reaction, presumably because the urease activity of the T-mycoplasmas released enough ammonia to inhibit the ammonia-sensitive components of the complement system. It was anticipated, and the present paper shows, that a similar mycoplasmacidal reaction exists for Mycoplasma hominis and specific antibody, and that this is dependent upon the concentration of arginine in the medium.This mycoplasmacidal reaction was then compared with complementindependent reactions of M . hominis and specific antibody, the latter including agglutination, metabolic inhibition, agglutination during growth, and inhibition of multiplication. The different types of interaction between M. hominis and specific antibody are recorded in detail and provide a basis for future studies of the specificity and sensitivity of the various types of interaction, as well as for the development of procedures for serotyping and for the study of antibody responses to M . hominis.
MATERIALS AND METHODSM . hominis, strain 4195, was isolated from the genital tract of a pregnant woman and was purified three times by a terminal dilution method. The mycoplasmas were grown in the basic medium {PPLO broth 70% (v/v), horse serum 20% (v/v), yeast extract 10% (v/v), phenol red 0.02% (w/v) and benzylpenicillin 500 U per ml, pH 7.2) supplemented with arginine 1 % (w/v). The growth of the organisms was indicated by increased pH of the medium as the arginine was deaminated. Titrations of the mycoplasmas were performed in microtitration plates and the results expressed as 50% colour-change units (CCU; Lin and Kass, 1970). A single pool of an overnight culture, stored at -7O"C, was used throughout this study.To prepare antigens for immunisation, overnight cultures containing approximately 108-9 CCU per ml were concentrated 100 times by centrifugation at 15,000 g for 30 min. at 4°C and stored at -20°C. Rabbits were immunised as previously described (Lin and Kass, 1970), each animal receiving about 1011 CCU of organisms. Antisera from two rabbits were pooled for use. Rabbit antisera from animals immunised against M. hominis (strain PG21) or M. arthritidis (strain PG27), and guinea-pig complement, were purchased commercially. Control antisera were obtained from rabbits immunised with concentrates of uninoculated
