<italic>Toxoplasma gondii</italic> rhoptry protein38 (TgROP38) affects parasite invasion, egress, and induces IL-18 secretion during early infection

Toxoplasma rhoptry protein 38 (TgROP38) is a new active kinase that modulates host cell signal transduction and TgROP38 expression shows strain-specificity and stage-specificity in different isolates. In the present study, we overexpressed ROP38 in the RH and prugniaud (PRU) strain (RH+rop38II and PRU+rop38II), disrupted ROP38 (PRUΔROP38) in the PRU strain, complemented the ROP38 (PRUΔROP38comp+) in the PRUΔROP38 strain, and compared phenotypes of gene-edited and parental strains. We found that knockout of ROP38 led to increased proliferation (P < 0.01) and invasion (P < 0.01) ability of the parasite. However, intraperitoneal infection with 1000 tachyzoites, PRUΔROP38 showed almost no virulent to mice compared with PRU (P < 0.01). Mice infected with low dose of PRU parasites produced higher levels of IL-18 and IL-1β compared with those infected with the PRUΔROP38 parasites during early days (P < 0.01). IL-18 produced by the PRU-infected group was significantly higher than that of the PRUΔROP38-infected group in vitro (P < 0.01). These phenomena may be related to the involvement of TgROP38 in the regulation of TgProfilin (TgPRF) protein, which could be recognized by host Toll-like receptor 11 and 12 (TLR11 and TLR12), an activation of host immune response. We also found that TgPRF expression was obviously decreased in PRUΔROP38, which was related to the cytokines production in mice model. These findings reveal an intriguing biological function of ROP38 in the RH and PRU toxoplasma, which may provide us with some clues of the existence of this protein in other isolates.