Thrombospondin binds normally to glycoprotein IIIb deficient platelets.

Glycoprotein IIIb (GPIV, CD36) has been proposed as the platelet receptor for thrombospondin (TSP). We found two healthy blood donors, whose platelets were shown to be GPIIIb deficient. These platelets expressed endogeneous TSP as control platelets and their binding capacity for exogeneous TSP was the same. These results indicate that GPIIIb is not the major TSP receptor on platelets. However, it is not yet possible to exclude that in GPIIIb-deficient platelets other proteins may substitute for GPIIIb in TSP binding.

Defective neutrophil and lymphocyte function in leucocyte adhesion deficiency.

We report a Chinese girl with the moderate phenotype of leucocyte adhesion deficiency (LAD), presenting with persistent omphalitis and recurrent soft tissue infections. She had subnormal adhesion-dependent neutrophil functions, such as chemotaxis and chemiluminescence response to a particulate stimulant (opsonised zymosan). Despite her adequate humoral response to documented herpes simplex virus type 1, parainfluenza type 2 and adenovirus infection in vivo, there was marked impairment in the generation of plaque-forming cells (PFC) driven by pokeweed mitogen (PWM) in vitro. IgM PFC were less severely affected than IgG and IgA PFC, probably because IgM production is less dependent on T cell help than IgA and IgG production. The patient's B cells and accessory cells had reduced function compared with the control subsets, while helper function of her CD4+ cells was virtually absent in the PWM-driven PFC assay. She also had marked defect in natural killer cell activity. The proliferation of her lymphocytes was normal to several plant lectins, including phytohaemagglutinin, concanavalin A and PWM, but markedly defective to OKT3.

[Paroxysmal nocturnal hemoglobinuria (PNH) deficiency of major complement-regulatory membrane proteins on erythrocytes].

The significance of the deficiency of the major complement-regulatory membrane proteins, decay-accelerating factor (DAF) and CD59, to the lysis of paroxysmal nocturnal hemoglobinuria (PNH) red blood cells was investigated. DAF and CD59 were demonstrated to be deficient simultaneously on affected PNH red blood cells (PNH-III) by two-color FACS analysis. At least in some patients with PNH, PNH-I was also revealed to be deficient partially in DAF. Purified DAF and CD59 ameliorated the complement sensitivity of PNH red blood cells, partially and completely, respectively. Functional blocking of these molecules on nomrla human red cells by monoclonal antibodies to DAF and CD59 rendered A or AB type blood cells complement-sensitive but not O or B blood type blood cells. The differences of complement-sensitivity among blood types were revealed to reside on the step of binding of C9 to C5b-8, i. e. C9 can bind to C5b-8 more on A type blood cells than on O type blood cells. We conclude that the deficiency of DAF and CD59 play a major role for the complement sensitivity of PNH red blood cells and that other factors reported to be deficient in PNH do less than these two proteins.

Role of CD11/CD18 in adhesion and transendothelial migration of T cells. Analysis utilizing CD18-deficient T cell clones.

The role of leukocyte function-associated Ag-1 (LFA-1) (CD11a/CD18) in T cell-endothelial cell (EC) interactions was assessed by utilizing CD11a/CD18-deficient T cell clones generated from a patient with leukocyte adhesion deficiency (LAD). The ability of these clones to bind to and migrate through monolayers of EC in vitro was compared with that of clones generated in a similar manner from normal controls. The LAD clones bound to EC to a similar extent as the controls. The contribution of other cell surface adhesion molecules was assessed with mAb blocking experiments. It was found that part of the EC binding by these CD11a/CD18-deficient clones was mediated by an interaction of very late Ag-4 (VLA-4) with vascular cell adhesion molecule-1 (VCAM-1) on the EC. In contrast to their normal ability to bind to EC, the capacity of the LAD clones to migrate through EC monolayers was significantly less than that of the control clones. This impairment in migration was not related to decreased intrinsic motility. Moreover, neither phorbol ester stimulation of the LAD clones nor IL-1 stimulation of the EC increased the capacity of the clones to migrate through EC monolayers, although binding to EC was augmented by both treatments. Only a minimal percentage of the migration of either control or LAD clones was inhibited by mAb to VLA-4 or VCAM-1. These data demonstrate that LFA-1 plays a central role in the transendothelial migration of T cells. In the absence of LFA-1, T cells retain the ability to bind to EC because of the activity of other receptor/ligand pairs, including VLA-4/VCAM-1. Finally, it is likely that, during both binding and transendothelial migration of T cells, additional cell surface molecules play a role.

CD18-deficient cells respond to lipopolysaccharide in vitro.

The CD11/CD18 complex of leukocyte adhesion molecules has been shown to bind LPS on the surface of gram negative bacteria and LPS-coated erythrocytes (J. Exp. Med. 164:1876, 1986). LPS elicits several responses in leukocytes including secretion of TNF-alpha and IL-1 beta, and priming for enhanced release of oxygen radicals such as superoxide anion. To determine if expression of CD18 molecules is necessary for these effects of LPS, we have examined the responses of leukocytes from CD18-deficient patients. Three of the patients in this study are characterized for the first time here, and three were described elsewhere. Monocytes and macrophages from CD18-deficient patients synthesized normal amounts of IL-1 beta and TNF-alpha in response to LPS. Further, PMN and monocytes from CD18-deficient patients showed normal priming for enhanced release of superoxide anion in response to LPS. Although a small contribution of CD18 molecules to some responses cannot be ruled out by our data, we may conclude that CD18 molecules are not essential for cellular responses to LPS.