[Lymphoblastic transformation by fractions of Brucella in patients having had brucellosis and subjects vaccinated by the vaccine PI].

Two fractions of brucella, examined elsewhere for their vaccinal properties (P.I. and 4A) have been used in lymphoblastic stimulation tests with lymphocytes of subjects infected by brucellosis and subjects vaccinated with P.I. This investigation attempted to show the importance of cellular immunity in brucellosis and to deduce a valid protection test. The two fractions do not possess non-specific mitogenic activity for human lymphocytes, but they stimulate specifically the sensitized lymphocytes. Subjects formerly or recently infected with brucellosis present constantly positive tests with sometimes a very high stimulation index. Vaccinated subjects have a lower stimulation index which is, however, significant in practically each case. The P.I. fraction gives the most constant results in the two categories of subjects; 4A appears to be much less active. The divergence between the protection rates conferred by 4A to animals and the weak activity of this same fraction in stimulation tests of human lymphocytes raises, on the one hand, the problem of the relation between protection and cellular immunity and, on the other hand, the utilization of animal models for the investigation of human vaccines.