Location of immunoglobulins and complement (C3) at the surface and within the skin of dogs

The serum proteins present at the skin surface in dogs were found to include the immunoglobulins (Ig) G, M and A, complement (C3) and albumin. Within the skin IgG and IgM were consistently found in the interstitial tissue throughout the dermis and were commonly present in the dermal blood vessels and hair papillae. IgA was undetectable or present in small amounts in the dermis in most of the 16 samples examined. It was found in the sweat glands, both in the lumen and the fundic epithelium, in some skin samples. C3 was demonstrated in the dermis and in the inter-cellular spaces of the stratum corneum. Elution of fresh skin specimens with phosphate buffered saline removed the majority of interstitial immunoglobulin and C3 from the dermis and some of the IgA from the sweat glands. IgM could still be demonstrated in the region of the epidermal basement membrane and C3 was not eluted from the stratum corneum. Removal of interstitial IgG and IgM facilitated the identification of immunoglobulin-bearing cells in the dermis. The distribution of IgG and IgM in dog skin is similar to that found in ruminants. Demonstration of IgA in the canine sweat gland fundus lends further support to the concept of IgA as a secretory immunoglobulin in the skin.