Topography of amphiregulin expression in cultured human keratinocytes: colocalization with the epidermal growth factor receptor and CD44.

Much of the autonomous growth of cultured keratinocytes is attributable to the signaling of amphiregulin, a heparin-binding autocrine growth factor, through the epidermal growth factor receptor. Emerging evidence suggests, moreover, that the membrane proteoglycan, CD44, is a cofactor for the interaction of heparin-binding ligands with their receptors. This model was evaluated by characterizing the patterns of the immunolabeled molecules in cultured human neonatal keratinocytes, to test the hypothesis that involvement in a common function results in coordinate segregation within or on the cell. The molecules were localized by double immunofluorescence labeling to detect amphiregulin and either the epidermal growth factor receptor or CD44, and the immunostained products were imaged by scanning laser confocal microscopy. Both amphiregulin and the epidermal growth factor receptor segregated to a perinuclear distribution and to intercellular contacts. In addition, amphiregulin localized to the outer leading edge of colonies and focally to intranuclear sites. Metabolic blockade of proteoglycan sulfation with sodium chlorate inhibited growth of the cells and concurrently enhanced the nuclear, but decreased the outer leading edge, labeling for amphiregulin. There was no nuclear or perimeter labeling for the epidermal growth factor receptor. Cultures co-immunolabeled for CD44 and amphiregulin exhibited variable perinuclear staining for both, but otherwise CD44 was distributed to intercellular contacts. The intercellular localizations of CD44 with amphiregulin and of amphiregulin with the epidermal growth factor receptor were strongly concordant. These data are consistent with a concerted function at intercellular contacts, where cytokine signaling is mediated via receptor binding and possibly regulated by the CD44 proteoglycan as cofactor. The intranuclear and perimeter labeling of amphiregulin, however, suggests that this cytokine has additional functions, both in the nucleus and as a matrix receptor.

Successful management of Mycoplasma hominis septic arthritis involving a cementless prosthesis.

PIP: Prompt identification of the infectious agent and antibiotic treatment are essential to the prevention of mortality or serious morbidity in patients with septic arthritis. Of concern is the increasing incidence of Mycoplasma hominis saprophytes as a cause of joint infections given the problems in isolating these microbes. The case of a 32-year-old black woman with a 9-year history of systemic lupus erythematous who presented with an M hominis-related septic arthritis involving hip and knee joint protheses offers guidelines on the predisposing factors and characteristic clinical and laboratory findings in such cases. The literature indicates that hypogammaglobulinemia, immunocompromise, postpartum or postabortion fever, and urinary tract manipulation are the risk factors most commonly associated with mycoplasmal septic arthritis. Typical laboratory results include a synovial fluid white blood cell count exceeding 80,000/mm3, a synovial fluid smear greater than 95% neutrophils, negative Gram's stain of synovial fluid smear, positive acridine-orange stain, and slow or absent growth in standard culture media. M hominis infections respond to tetracyclines, lincomycin, and clindamycin, but are resistant to erythromycin. Risk factors in the patient described here included longterm corticosteroid treatment, prior urinary tract infection, and an abortion 2 months prior to presentation for which antibiotic prophylaxis was not administered. The results of synovial tissue, bone, and irrigation fluid cultures were initially negative, but more sophisticated testing ("fried egg" morphology) isolated M hominis. This microorganism was also isolated in endometrial tissue cultures, and retained products of conception are considered the most likely source of the patient's joint infection. A 10-week course of tetracycline eliminated the infection.^ieng