Electron microscopic studies of human monocyte and lymphocyte interaction with immunoglobulin- and complement-coated erythrocytes

Electron microscopic studies of the interaction of human monocytes and lymphocytes with erythrocytes coated with IgG and complement have been performed using the lanthanum colloid tracer and ferritin-labelled antibody techniques. Interaction between monocytes and IgG coated erythrocytes results in rosette formation with a space of 400 Å between opposing monocyte-erythrocyte membranes. Zones of interaction occurred with a periodicity which corresponded to the erythrocyte Rho antigenic sites. When monocytes are incubated with complement coated red cells erythrophagocytosis occurs. The rosettes which form between complement coated red cells and about 20% of human blood lymphocytes differ from monocyte rosettes and show zones of contact separated by spaces of 100–200 Å. The lanthanum colloid tracer penetrates the broad zones of attachment between opposing lymphocyte-erythrocyte membranes; the presence of areas devoid of lanthanum suggests the possibility of discrete subunits in these zones which may be similar to junctional type structures. The type of interaction observed with complement receptor lymphocytes may be important in cell-cell interaction in the immune response.