Morphometric and ultrastructural analyses of in vivo-activated murine Langerhans cells induced by administration of a streptococcal preparation (OK-432).

Langerhans cells (LCs) are activated in the epidermis by external and internal stimuli, such as antigens and cytokines, respectively. To reveal the morphologic and functional properties of in vivo-activated LCs during inflammation, we injected the streptococcal preparation OK-432 intradermally into the earskin of mice and performed time-course analyses by immunofluorescence and electron microscopy. Cellular infiltrate appeared in the dermis at 6 h after OK-432 injection and had progressively extended to the dermoepidermal junction at 12 and 24 h. Immunostaining for class II antigen revealed that LCs were enlarged and extended long dendrites during inflammation. Acidic compartments such as lysosomes and multivesicular bodies also increased in number and Golgi apparatuses developed as demonstrated by electron microscopy and morphometric analysis. Birbeck granules, although not showing numerical changes, were translocated from the Golgi area to the subplasmalemmal area. After epicutaneous application of cationic ferritin, LCs often contained endosomes as the result of engulfment by the cytoplasmic projections. The present results indicate that nonspecifically induced dermal inflammation is capable of inducing activation of LCs in vivo, and that in vivo-activated LCs have the capacity for active endocytosis and intracellular digestion or processing.