Giardia muris-induced depression of the primary immune response in spleen and mesenteric lymph node cell cultures to sheep red blood cells.

Primary in vitro plaque-forming cell (PFC) responses to sheep red blood cells (SRBC) were examined for spleen and mesenteric lymph node (MLN) cell populations from susceptible (A/J) and resistant (B10.A) mice during the infection with Giardia muris. Spleen and MLN cells isolated from mice during the acute phase of the infection were less responsive to SRBC in vitro than those from uninfected mice. Depressed anti-SRBC PFC response was detected earlier and was more pronounced in MLN cell cultures when compared to the response of spleen cell cultures. Spleen and MLN cells from donors infected with G. muris for 15 days had the capacity of depressing PFC response to SRBC of cells isolated from uninfected mice. This suppressor activity was localized in the plastic-adherent fraction of spleen cell populations isolated from A/J and B10.A mice. Since G. muris is a gastro-intestinal infection of mice, lower capacity of the MLN cells to respond to an antigenic stimulation in vitro may explain, in part, the proliferation of the trophozoites during the acute phase of the infection.