Bispecific cells among IgM and IgG producers during the early phase of primary and secondary responses

Abstract

Simultaneous immunization of mice with sheep (SRBC) and horse (HRBC) erythrocytes regularly resulted in the appearance of hemolytic plaque-forming cells (PFC) specific for each type of erythrocyte and also of PFC lysing both types of erythrocytes. After primary stimulation the highest number of bispecific cells (42/10(6) cells) was found among PFC as revealed by the direct procedure (IgM producers). Among PFC enhanced with anti-mouse Fab serum (IgG producers), bispecific cells were less numerous (8/10(6) cells). In preparations enhanced by anti-mouse-gammaFc serum which reveals IgG producers without inhibiting IgM antibody, the number of bispecific PFC equalled the sum of bispecific cells revealed by direct and anti-Fab enhanced procedures. The number of direct bispecific PFC during primary and secondary response was approximately the same, whereas the number of IgG-producing, bispecific PFC increased considerably during the secondary response. Another difference was the time limitation of the appearance of bispecific cells: after primary immunization direct bispecific PFC were detected only on days 3, 4 and 5, but enhanced bispecific PFC were present from day 4 up to day 12. However, during the secondary reaction, bispecific PFC were detected by all three procedures only between days 3 and 6. Studies on the cross-reactivity between SRC and HRBC gave negative results at the humoral level, even when the mice were primed with a minimal amount of both erythrocytes and then two months later, boosted with one of them. Studies at the cellular level showed that after immunization with one antigen, only 0.4 to 0.7 direct or enhanced PFC/10(6) cells could simultaneously lyse both erythrocyte types. Thus, a hundred times more bispecific PFC were constantly found after double immunization of the animals. Moreover, sudden disappearance of all bispecific PFC on the 7th day after secondary stimulation makes it unlikely that all bispecific PFC are simply cross-reacting cells.

Un lymphocyte B – un anticorps : le dogme ébranlé

“…Concernant l'antigène GR, la réponse B primaire ou secondaire s'obtient quatre à cinq jours après l'injection en absence d'adjuvant. Nos études se sont donc surtout focalisées sur le début de la réponse « ex vivo » [8], mais aussi « in vitro » [9,10] entre les jours 2 et 6 après immunisation et toujours avec des doses d'antigènes non optimales, afin d'étu-dier un maximum de PFC formées d'immunoblastes en voie de différenciation. L'originalité de nos premières études consistait donc à décrire la cinétique de la réponse anticorps après immunisation de souris avec un mélange de globules rouges de mouton (GRM) et de globules rouges de pigeon (GRP), phénotypiquement distincts [11].…”