Fc-receptor variants of a mouse macrophage cell line

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Abstract
Variants of the J774 mouse macrophage cell line that lack immunologically important membrane receptors were isolated. After mutagenesis, variants were selected in a metrizamide gradient that separated cells heavily rosetted with sheep erythrocytes (E) coated with rabbit anti-E IgG (EIgG) from poorly rosetted cells. Stable variants that exhibited altered binding were found with a frequency of 20 per cell for J774. After trypsinization, three variants bound only three to five EIgG per cell; the J774 line was not affected by this treatment. Monomeric IgG2a could inhibit the binding of soluble rabbit IgG—antigen complexes to the variants but not to the parent line. Finally, E coated with IgM and complement (EIgMC) were bound poorly by all the variants, relative to the J774 parent. These results show that rabbit IgG complexes are bound by both FcRI and FcRII on mouse macrophages. The impairment of EIgMC rosetting in the variants suggests that the C3b receptor and FcRII are related.