Receptors for complement of Langerhans cells.

A population of guinea pig epidermal cells, identified as Langerhans cells, formed rosettes with sheep erythrocytes coated with IgM immunoglobulin and C3b (EAC1-3b) but not with intermediates carrying only C1, C14b, or C14b2a. These findings were unusual since most other cells expressing C3b receptors also express C4b receptors. To investigate whether these results were the consequence of a limited number of C4b molecules on the cells, EAC14b cells were prepared with increased amounts of C4b (15 to 250 micrograms on 10(9) cells). EAC14b rosette formation was found with a maximal number when there were 3,000 molecules per cell, a 6-fold excess over that found in previous experiments. One could inhibit this rosette formation by fluid phase C3b as well as by fluid phase C4b, suggesting proximity or possible identity of these 2 receptors.