Langerhans cells (LC) constitute a small proportion of the mammalian epidermal cells and may be identified by their unique ultrastructural appearance. Of all the cells in the guinea pig epidermis, only Langerhans cells—as defined by ultrastructural criteria—form rosettes with IgG antibody-coated BRBC. Using this rosette assay for the identification of LC and an indirect immunofluorescent technique with FITC-SPA as a marker to detect antigens of the guinea pig MHC, we have investigated whether guinea pig LC bear Ia antigens. Rosette-forming epidermal cells (RF-EC)—identical to LC—from strain 2 animals bound only an anti-strain 2 antiserum, but not an anti-strain 13 antiserum or NGPS and, in reverse fashion, RF-EC from strain 13 animals bound an anti-strain 13 antiserum, but not an anti-strain 2 antiserum or NGPS. LC from (2 × 13)F1 animals reacted with both an anti-strain 2 and anti-strain 13 antiserum, but not with NGPS. Non-RF-EC did not bind any of the anti-Ia antisera. An anti-B.1 antiserum, by contrast, reacted with all epidermal cells from strain 2, strain 13, and (2 × 13)F1 animals (known to share in common B.1 antigens), but not with epidermal cells from a B.3 animal. These results demonstrate that Ia antigens in guinea pig epidermis are selectively expressed on LC, whereas GPLA-B region antigens can be detected on all epidermal cells. Fc-IgG rosette formation by LC can be inhibited by either the specific anti-Ia antiserum or by specific anti-B region antisera, which seems to indicate that antibodies against various antigenic determinants on LC may provoke subtle membrane changes resulting in Fc receptor blockade.

The finding of Fc receptors along with the expression of Ia antigens on the surface of LC supports the concept of their being involved in the afferent limb of the immune response.

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