The effect of prolactin (PRL) on the growth of Toxoplasma gondii tachyzoites in vitro

During the development and effector phases of the anti-Toxoplasma response, the immunological system of a host is involved in several complex interactions with the endocrine system, and prolactin (PRL) is one of the most important hormones involved in immunoregulation. In this work, the influence of the recombinant human prolactin (rhPRL) on the viability, penetration, and intensity of intracellular proliferation of Toxoplasma gondii BK strain in vitro was evaluated. Using one murine (L929) and two human cell lines (Hs27 and HeLa), no toxic effect of the rhPRL on host cells was found (by determining cellular viability using MTT assay). A similar lack of rhPRL cytotoxic activity was found in the case of the extracellular tachyzoites of T. gondii BK. Replication of parasites in the presence of rhPRL was analyzed first by simultaneous addition of the hormone and the parasites into a microculture of the host cells (treatment during infection). No statistically significant changes in the intensity of parasite proliferation in all used host cells were found for a wide range of the hormone concentrations. However, pre-incubation of the tachyzoites with rhPRL resulted in a significant reduction (up to 36.15%) in the replication abilities of the parasite. Further experiments revealed that in fact, the inhibition of replication was caused by a limited capacity of the parasites to penetrate host’s cells as demonstrated by the reduced number of infected cells.