ENHANCED IN-VITRO ENGULFMENT OF LISTERIA-MONOCYTOGENES BY RABBIT POLYMORPHONUCLEAR LEUKOCYTES IN THE PRESENCE OF SERA FROM IMMUNE RABBITS

The role of immune serum in the engulfment of Listeria monocytogenes b y polymorphonuclear leukocytes (PMNLs) of rabbits was documented emplo ying an in vitro assay. Three serovarieties of L. monocytogenes, via. serovars 1/2a, 4a and 4b, were separately incubated with PMNLs of noni mmune rabbit and high titre homologous or heterologous antisera. Norma l rabbit serum was used as control. The number of L. monocytogenes per neutrophil was counted in stained smears in each assay and opsonic in dices were calculated. Higher opsonic indices, i.e. 2.50, 2.09 and 2.5 6, for the three strains respectively, were obtained when bacteria wer e engulfed in the presence of homologous antisera as compared to when the bacterial cells were incubated with heterologous antisera, opsonic indices being in the range of 0.87 to 1.63. These results are indicat ive of a possible role of specific serum factors in at least the inter nalization of L. monocytogenes by PMNLs of rabbits and therefore in th e host defenses against Listerial infections.