Passive haemagglutination tests using purified antigens covalently coupled to turkey erythrocytes.

: Passive haemagglutination tests have been developed by covalent coupling purified antigens to turkey red blood cells. Circulating antibodies can be assessed in 20 minutes using one drop of blood. False positive reactions are avoided by using highly purified antigens; sensitized erythrocytes are stable in the absence of freeze-drying and blood samples can be preserved on paper discs. This method, applied to the determination of circulating tetanus (T) and diphtheria (D) antibodies and titres compared to other in vivo or in vitro methods, gave good correlation. The titration of circulating antibodies can be applied in emergency care units and field trials to establish whether the individuals are adequately protected. Results of surveys by several health care centres have shown that tetanus immune coverage was insufficient in France. The decrease of both T and D immune coverage with age has been established. The antibody response of pregnant women, vaccinated with two different adsorbed T toxoids exhibiting a low and a high titre as expressed in international immunizing units (I.I.U.), was studied. No significant difference in circulating antibody titres was obtained after the first injection of either vaccine, but titres after second injection were much higher for the vaccine having a low value expressed in I.I.U. The activity of commercial and reference T vaccines can be evaluated in mice after immunization and titration of the antitoxin levels. This simple method is much easier than the official evolution of immunodeficiency in certain diseases. The passive haemagglutination test has also been used to measure anti-HBs and anti-gp 160 antibodies.