Ia Antigens and Fc Receptors of Mouse Peritoneal Macrophages as Determinants of Susceptibility to Lactic Dehydrogenase Virus

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Abstract
The relationship between susceptibility of mouse peritoneal macrophages to lactic dehydrogenase-elevating virus (LDV) infection and expression of I region-coded antigens (Ia) on these cells was investigated. The proportions of Ia-positive cells in resident peritoneal macrophages from adult and suckling mice were 4-10% and 50-70%, respectively. Approximately the same percentages of the cells were susceptible to LDV, as detected by fluorescent antibody staining. In adult mice, double-labeling experiments showed that most of the Ia-positive cells were LDV-infected. When the cells were cultured for > 24 h in vitro, Ia-positive cells rapidly disappeared and the culture became resistant to LDV. Removal of Ia-positive cells by treatment with anti-Ia plus complement or enrichment using an anti-Ia-coated petri dish simultaneously removed or enriched for LDV-susceptible cells. Treatment of cells with trypsin (1 mg/ml) removed their I-A and I-E antigens and simultaneously abolished susceptibility for LDV. When LDV was preincubated with subneutralizing amounts of antibody, infectivity of macrophages was enhanced and the proportion of LDV-infected cells was higher than that of Ia-positive cells. This suggests that Fc receptors on macrophages can act as receptors for LDV coated with antiviral IgG.