The Action of Phytohemagglutinin in Rabbits. V. Morphological Changes Following Previous Immunization with and Daily Injections of Phytohemagglutinin

The administration of a series of four or eight daily injections of PHA neither diminished nor enhanced the peripheral and parenchymal changes observed after a single injection of PHA. These changes include the peripheral leukopenia followed by a leukocytosis, the hyperplasia of the splenic white pulp, and the myeloid metaplasia or infiltration in the splenic red pulp.

The circulating leukocytes appear to become resistant to the leukopenic action of PHA following a series of injections of PHA. However, this stage of refractoriness lasts only one to two weeks in the absence of any further injection of PHA.

Immunization with PHA with formation of antibodies capable of neutralizing the mitogenic factor(s) in PHA did not affect the capacity of a subsequent challenge injection of PHA to induce the characteristic morphologic changes which follow a single injection of PHA. Thus, the presence of circulating antibodies does not invalidate the use of PHA as a chemotherapeutic agent.