The molecular basis of target cell recognition by CD3- natural killer (NK) cells is poorly understood, despite the ability of NK cells to lyse specific tumour cells. In general, target cell major histocompatibility complex (MHC) class I antigen expression correlates with resistance to NK cell-mediated lysis, possibly because NK cell-surface molecules engage MHC class I antigens and consequently deliver inhibitory signals. Natural killer cell allospecificity involves the MHC class I peptide-binding cleft, and further understanding of this allospecificity should provide insight into the molecular mechanisms of NK cell recognition. The Ly-49 cell surface molecular mechanisms of NK cell recognition. The Ly-49 cell surface molecule is expressed by 20% of CD3- NK cells in C57BL/6 mice (H-2b). Here we show that C57BL/6-derived, interleukin-2-activated NK cells expressing Ly-49 do not lyse target cells displaying H-2d or H-2k despite efficient spontaneous lysis by Ly-49- effector cells. This preferential resistance correlates with expression of target cell MHC class I antigens. Transfection and expression of H-2Dd, but not H-2Kd or H-2Ld, renders a susceptible target (H-2b) resistant to Ly-49+ effector cells. The transfected resistance is abrogated by monoclonal antibodies directed against Ly-49 or the alpha 1/alpha 2 domains of H-2Dd, suggesting that Ly-49 specifically interacts with the peptide-binding domains of the MHC class I alloantigen, H-2Dd. Inasmuch as Ly-49+ effector cells cannot be stimulated to lyse H-2Dd targets, our results indicate that NK cells may possess inhibitory receptors that specifically recognize MHC class I antigens.

De novo lymphangiogenesis influences the course of different human diseases as diverse as chronic renal transplant rejection and tumor metastasis. The cellular mechanisms of lymphangiogenesis in human diseases are currently unknown, and could involve division of local preexisting endothelial cells or incorporation of circulating progenitors. We analyzed renal tissues of individuals with gender-mismatched transplants who had transplant rejection and high rates of overall lymphatic endothelial proliferation as well as massive chronic inflammation. Donor-derived cells were detected by in situ hybridization of the Y chromosome. We compared these tissues with biopsies of essentially normal skin and intestine, and two rare carcinomas with low rates of lymphatic endothelial proliferation that were derived from individuals with gender-mismatched bone marrow transplants. Here, we provide evidence for the participation of recipient-derived lymphatic progenitor cells in renal transplants. In contrast, lymphatic vessels of normal tissues and those around post-transplant carcinomas did not incorporate donor-derived progenitors. This indicates a stepwise mechanism of inflammation-associated de novo lymphangiogenesis, implying that potential lymphatic progenitor cells derive from the circulation, transmigrate through the connective tissue stroma, presumably in the form of macrophages, and finally incorporate into the growing lymphatic vessel.

SummaryAutoimmune bullous skin disorders are induced by autoantibodies against distinct adhesion complexes of the epidermal and dermal-epidermal junction. Since most of these disorders are characterized by a severe, potentially lethal course, they require long-term immunosuppressive treatment to reduce the de novo synthesis of pathogenic autoantibodies by B lymphocytes. Rituximab, a chimeric monoclonal antibody against CD20 on B lymphocytes, has shown promise in several case reports or cohort studies in the treatment of paraneoplastic pemphigus, refractory cases of pemphigus vulgaris and foliaceus and in other autoimmune bullous disorders.Treatment with rituximab leads to depletion of pathogenic B-cells which may last up to 12 months resulting in a reduction of plasma cells secreting pathogenic autoantibodies. Rituximab is usually administered in an adjuvant setting at a dose of 375 mg/m 2 i. v. in weekly intervals for four consecutive weeks in addition to the standard immunosuppressive treatment. The present consensus statement of German-speaking dermatologists, rheumatologists and oncologists summarizes and evaluates the current evidence for the use and mode of application of rituximab in autoimmune bullous skin disorders.

Severe pustular psoriasis von Zumbusch type is a therapeutic challenge not only in adults, but even more in children. We report a 3(1/2)-year-old boy who developed a generalized flare of diffusely scattered pustules on erythematous skin which rapidly progressed to large exuding areas. The clinical presentation and investigations including histopathological examination of a biopsy and negative bacterial cultures were consistent with the diagnosis of pustular psoriasis von Zumbusch type. Upon initial treatment with methylprednisolone, acitretin and antibiotics the extent of the disease declined. However, several attempts to reduce the dose of the oral corticosteroid were followed by immediate severe flares. Additional treatment with narrowband ultraviolet B (NB-UVB, 311-313 nm UVB) resulted in a rapid arrest of disease activity and allowed the corticosteroid to be tapered off. After 10 irradiations the patient was both off steroid and disease free. NB-UVB therapy was subsequently reduced to twice-weekly exposures and acitretin gradually diminished to a maintenance dose of 0.3 mg kg(-1) daily. We conclude that NB-UVB in conjunction with acitretin is a potent therapeutic regimen for the treatment of severe pustular psoriasis von Zumbusch type in childhood.

Sllll~mal~Target cell expression of major histocompatibility complex (MHC) class I molecules correlates with resistance to lysis by natural killer (NK) cells. Prior functional studies of the murine NK cell surface molecule, Ly-49, suggested its role in downregulating NK cell cytotoxicity by specifically interacting with target cell H-2D d molecules. . Although the molecular basis for NK cell specificity is poorly understood, target cell susceptibility to spontaneous cytotoxicity is inversely proportional to their level of expression of certain MHC class I molecules (3-5). Two explanations (6) have been proposed. MHC class I molecules may "mask" or interfere with recognition of putative target cell ligands by activation receptors on NK cells. Alternatively, target cell MHC class I molecules may directly engage NK cell receptors leading to inhibitory events in NK ceils. Our previous functional studies (7) of the murine Ly-49 molecule have supported the latter hypothesis.Ly-49 is a type II integral membrane protein (8, 9), with an external C-type lectin domain (9), expressed on a distinct subset of murine NK cells (10) as a disulfide-linked homodimer of44-kD subunits (9). Functional studies with IL-2-activated NK cells demonstrated that Ly-49 + NK cells generally manifested a lytic capacity equivalent to Ly-49-NK cells (7). However, Ly-49 + NK cells were unable to lyse targets of H-2 k or H-2 d haplotype despite efficient lysis of these targets by Ly-49-NK cells, demonstrating that Ly-49 expression significantly influences NK cell target specificity. Transfection of a susceptible target cell line with cDNA encoding H-2D a rendered it resistant to lysis by Ly-49 + NK cells. Ly-49 + NK cells were unable to lyse the D a transfectant by other stimuli, including Ab-dependent cellular cytotoxicity (7, 11). Gene transferred resistance was abrogated by mAbs against either Ly-49 or the otl/o~2 domain of D a. These data were compatible with our hypothesis that Ly-49 is an inhibitory receptor that specifically recognizes D a molecules on targets.Our interpretation of t.hese functional studies predicts that Ly-49 directly interacts with H-2D d. Alternatively, the results may be explained by a NK cell surface molecule that is coexpressed with Ly-49 and that is indirectly influenced by the anti-Ly-49 mAb. Moreover, reversal of functional inhibition by mAbs could be due to other effects such as direct anti-Ly-49 triggering or anti-H-2D d dissociation of another effector cell ligand (12). A final possibility involves the "masking model" in which H-2D a masks another target molecule specifically recognized by . To distinguish between these possibilities, we sought to unequivocally establish the ligand for Ly-49. We have now overexpressed Ly-49 on Chinese hamster ovary (CHO) cells by transfection and DNA amplification. CHO cells bind target cells only when the cells express high levels of Ly-49 and H-2D a, respectively, by transfection. This interaction is specifically blocked by appropriate mAbs. Thus, this study demonstrates that...