Figure 6.

Blocking of the mast cell TNF-α response to FimH-expressing E. coli but not to IgE and antigen by pretreatment of BMMCs with antibodies to CD48 and with PLC. (A) Human gamma globulin-treated monolayers of BMMCs were incubated with indicated concentrations of antibody against either CD48 or CD117 (control) for 1 hr at 37°C, and then bacteria were added to the wells. TNF-α release from cell-free supernatants was measured after 1 hr. (B) BMMC suspensions were pretreated with indicated concentrations of PLC for 1 hr. The PLC was removed by repeated washing, and the BMMCs were seeded in wells of a 96 well tissue culture plate in the presence of 1 μM actinomycin D to form monolayers. After overnight incubation, the BMMC monolayers were exposed to FimH-expressing bacteria and the TNF-α released from cell-free supernatants was assayed after 1 hr. (C) To examine the TNF-α response of mast cells to IgE and antigen, untreated control BMMCs and BMMCs pretreated with PLC at 3 units/ml or CD48-specific antibody at 30 μg/ml were sensitized with anti-DNP IgE and subsequently challenged with DNP-BSA (antigen) at 50 ng/ml for 1 hr at 37°C. TNF-α released from cell-free supernatants was assayed thereafter. Data are the mean ± SEM values obtained from three experiments.