FASCIOLA HEPATICA-INDUCED IMMUNE SUPPRESSION OF SPLEEN MONONUCLEAR CELL-PROLIFERATION - ROLE OF NITRIC-OXIDE

The aim of the present study was to evaluate the proliferative respons e of spleen mononuclear cells (Spm) to mitogens in rats infected with Fasciola hepatica and its correlation with Spm and peritoneal cell (PC ) nitric oxide (NO) production on Days 1, 3, 7, 14, 30, and 60 postinf ection. In addition, histological changes in the liver were also studi ed. The proliferative response to Con A of F. hepatica-infected Spm wa s significantly decreased on Day 7 postinfection (P < 0.01). However, a pronounced increase of the proliferative response was detected from Day 3 until Day 60 when Spm were stimulated with LPS. In order to dete rmine whether NO levels were modified during P. hepatica infections, w e quantified nitrite in Spm and PC supernatants in cultures. Our resul ts indicate a profound decrease of nitrite production by LPS-stimulate d PC on the first and second weeks postinfection, and an increase in t he levels of this mediator on LPS-stimulated Spm at the same postinfec tion time. The F. hepatica excretory-secretory antigen (ESA) was in pa rt involved in the decrease of nitrite production by LPS-stimulated PC . A mechanism to avoid an immune response during the first stages of l iver penetration could explain the transient suppression observed in S pm proliferative responses. On the either hand, the decrease in NO pro duction by rat-infected PC could also be one of the strategies of the parasite to avoid the potential killing effect of NO during peritoneal migration. (C) 1998 Academic Press.