Previously, a hypomorphic mutation in CD18 was generated by gene targeting, with homozygous mice displaying increased circulating neutrophil counts, defects in the response to chemically induced peritonitis, and delays in transplantation rejection. When this mutation was backcrossed onto the PL/J inbred strain, virtually all homozygous mice developed a chronic inflammatory skin disease with a mean age of onset of 11 weeks after birth. The disease was characterized by erythema, hair loss, and the development of scales and crusts. The histopathology revealed hyperplasia of the epidermis, subcorneal microabscesses, orthohyperkeratosis, parakeratosis, and lymphocyte exocytosis, which are features in common with human psoriasis and other hyperproliferative inflammatory skin disorders. Repetitive cultures failed to demonstrate bacterial or fungal organisms potentially involved in the pathogenesis of this disease, and the dermatitis resolved rapidly after subcutaneous administration of dexamethasone. Homozygous mutant mice on a (PL/J x C57BL/6J)F1 background did not develop the disease and backcross experiments suggest that a small number of genes (perhaps as few as one), in addition to CD18, determine susceptibility to the disorder. This phenotype provides a model for inflammatory skin disorders, may have general relevance to polygenic human inflammatory diseases, and should help to identify genes that interact with the 82 integrins in inflammatory processes.A large number of leukocyte and endothelial cell adhesion molecules are known to play a role in inflammatory processes, leukocyte trafficking, and immune responses (1). The molecules include immunoglobulin family members such as intercellular adhesion molecule 1 (ICAM-1), the selectins, selectin ligands, and leukocyte integrins (1). The P2 leukocyte integrins are heterodimers of CD18 with one of three CD11 subunits:LFA-1 (CD18/CD11a), Mac-1 (CD18/CD11b), and p150/95 (CD18/CD11c). Mutations in CD18 have been reported in humans (2, 3) and in cattle (4, 5) and result in the lifethreatening disorder termed leukocyte adhesion deficiency type I. CD18-deficient patients suffer from recurrent microbial infections, leukocytosis, impaired wound healing, failure of granulocyte -emigration, and lack of pus formation (2, 3). Severe and moderate phenotypes have been described in humans, and the severity of the phenotype appears to correlate with the presence of null or hypomorphic mutations, respectively (3, 6).Previously, a hypomorphic mutation for CD18 was introduced into mice with homozygotes displaying mild leukocytosis, an impaired response to chemically induced peritonitis, and delays in transplantation rejection (7). These mice express a low level of normal CD18 on leukocytes with 2-16% ofThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.wild-type levels of CD18 expression on resting or activated leukocytes...

Microbial flora of the skin of three human population groups representing different natural environments was examined quantitatively and qualitatively to determine whether environmental differences in temperature and humidity can influence the microbial flora of normal skin. Five anatomical skin sites - hands, back, axillae, groin, and feet - were sampled from 10 subjects working in a high-humidity, high-temperature environment, 10 subjects from a low-temperature, high-humidity environment, and 10 subjects working in a moderate-temperature and low-humidity environment. Bacterial populations were significantly larger from the back, axillae, and feet in individuals from the high-temperature and high-humidity environment as compared to the moderate-temperature, low-humidity environment. High humidity and low temperature had no significant effect on total populations, but this group showed a higher frequency of isolation of fungi, and gram-negative bacteria from the back and feet. Although there was an indication that increase in the environmental humidity could result in an increased frequency of isolation of gram-negative bacteria, there was no evidence that an increase in either temperature or humidity altered the relative proportions of gram-negative bacteria in the predominantly gram-positive microbial flora found on normal skin. It was concluded that, although climatic changes may cause fluctation in microbial populations from certain sites, they are not a major influence on the ecology of the microbial flora of normal skin in the natural environment. The variables introduced by studying individuals in their natural environment and the influence of these on the results are discussed.

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Summary.A new aerobic gram-positive non-sporeforming bacillus has been isolated from infected genital hair of patients with white piedra in association with Trichosporon beigelii. This species has been characterised morphologically, nutritionally, by DNA base composition, cell-wall analysis and cellular fatty-acid profile on the basis of 14 isolates. The G + C content of DNA is 63-05 mol Yo. Cell walls possess meso-diaminopimelic acid (Type IV) and the sugars glucose, galactose, xylose and ribose ; mycolic acids are not present. The species has a distinct colonial and microscopic morphology, is strongly proteolytic and produces methanethiol. These findings and the cellular fatty-acid profile are compatible with the genus Brevibacterium. A new species is proposed based on the following characters : colonial and microscopic growth and morphology ; conditions for rod-to-coccus cycle ; ribose utilisation ; and tellurite reduction. The type strain has been named Brevibacterium rncbrellneri E2cr (ATCC 49030). The strong proteolytic properties may be the mechanism of pathogenesis.