Neutralization test carried on a non-nutrient blond agar prepared from sheep erythrocytes sensibilized with equi factor of Rhodococcus equi was used for the detection of antibodies against phospholipase D (PLD) of Arcanobacterium haemolyticum. Altogether, 433 sera from 404 patients aged 1 to 25 years with the signs of acute tonsillitis were examined. Antibodies against PLD were found in 28 patients (6.9 %). In 116 sera from persons without the signs of tonsillitis the antibodies against PLD were detected in one tase (0.9 %). The titres reached the values from 4 to 1i4. Out of 84 paired sera, the significant change of the titre, i.e. at least the four-fold one, was observed five times: three times as the seroconversions, twice as the declines of the titre. The antibodies were found most often in children aged 11 to 15 years, 10 times out of 97 (10.3 %). In 253 patients with the tonsillitis, the result of the parallel bacteriologic examinations of throat swabs was at the disposal. A. haemolyticum was successfully isolated in 3 cases, but only owing to the inhibition of staphylococcal hemolysis around its colonies. All three cases were also serologically positive. Consequently, our results show that neutralizing antibodies against PLD ofA. haemolyticum can be detected in patients with tonsillitis.

        Key words: Arcanobacterium haemolyticum - antibodies - neutralization test - phospholipase D - equi factor - acute tonsillitis.