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The ICAM-1 molecule is an important adhesion factor that facilitates lymphocyte activation as well as the movement of lymphocytes into solid tissues. It is poorly expressed on circulating monocytes but higher levels have been described following the use of some activation factors. While previous work has emphasized the role of interferon gamma in inducing increased ICAM-1 expression on nonleukocytic cells, we have demonstrated time- and dose-dependent increases on human monocytes and two myelomonocytic cell lines (Rc2A & U937). The increased level of ICAM-1 expression on the Rc2A cells was associated with higher accessory cell activity as determined by an increased mitogen and allogeneic response but specific antibody inhibition studies indicated only a partial dependence (up to 50%) on this molecule. Class II MHC expression and IL-1 production were not elevated by IFNg treatment of these cells, indicating that other factors account for the remainder of the incremental activity observed following this treatment.

The distribution of HLA-ABC and DR antigens in human kidneys was studied using monoclonal antibodies to monomorphic determinants and a 4-layer immunoperoxidase technique applied to frozen and paraffin sections. Enzyme digested paraffin sections provided the best localization. HLA-ABC antigens were located on all renal endothelium, Bowman's capsule and in proximal tubules. HLA-DR antigen was restricted to capillary and venous endothelium plus, at low density, in proximal tubules. Minor differences in distribution were found with different monoclonal antibodies, but dendritic cells were not detected using monoclonal antibodies to HLA-ABC, HLA-DR or leukocyte-common antigens.

The monoclonal antibody PHM-6, which is specific for the common acute lymphoblastic leukemia antigen (CALLA), was conjugated to the plant toxin ricin. Binding of the PHM-6-ricin conjugate to cells via the ricin molecule was blocked by the presence of 100 mM lactose. The IC50 (concentration resulting in 50% inhibition) of the PHM-6-ricin conjugate for the CALLA-positive KM-3 cell line was 280-fold greater than for bone marrow stem cells, indicating the potential of this conjugate for immunological purging of autologous remission marrow.

Three monoclonal antibodies have been made to identify cells of the human mononuclear phagocyte system in fluids and tissues. The first, PHM 1, recognises a surface antigen common to all leucocytes. The other 2 antibodies, PHM 2 and PHM 3, bind to monocytes and macrophages but not to polymorphonuclear cells (PMN). PHM 2 labels all monocytes, macrophages and a small population of T-cells. PHM 3 labels most monocytes and macrophages but no other blood cells. The application of these monoclonal antibodies to the identification of mononuclear phagocytes in blood and liver using an unlabelled antibody immunoperoxidase (PAP) technique is demonstrated.

The in vitro response of human lymphocytes to phytohaemagglutinin was inhibited in a dose-related fashion by methylprednisolone added to the cell culture. The inhibition by steroid was 100-fold less than expected from published values of human lymphocyte receptor affinity. The dose response curve for inhibition was complex, frequently featuring a plateau region suggestive of a heterogeneous system, possibly caused by the presence of more than one subpopulation of cells. When lymphocytes were separated by unit velocity sedimentation, slow sedimenting lymphocytes were found to be highly steroid sensitive whereas rapidly sedimenting lymphocytes were steroid resistant. However, the addition of cultured macrophages rendered the steroid-sensitive fractions relatively steroid resistant. Similarly, unseparated peripheral blood lymphocytes at low concentrations were found to be highly steroid sensitive despite the addition of 2-mercaptoethanol. This sensitivity was lost by the addition of culture macrophages. Thus, macrophages play a vital role in the relative steroid resistance of human lymphocytes. No evidence was found that macrophages actually reduced steroid concentration in culture, and it is suggested that a cellular interaction is required to increase resistance to steroids.

A series of monoclonal antibodies to human glomerular antigens was prepared by immunisation of a mouse with isolated whole glomeruli, followed by boosting with particulate glomerular basement membrane and fusion of murine spleen cells with the NSI-myeloma line. Hybridoma supernatants were screened jointly by a radioimmunoassay involving binding to isolated glomeruli, and by a 4-layer immunoperoxidase technique applied to polyester wax-embedded sections. Seven monoclonal antibodies with different specificities (PHM7-PHM13) were established and repeatedly cloned. Each antibody displayed a distinctive distribution within the glomerulus, including different patterns of staining of mesangial cells, mesangial matrix and glomerular basement membrane, in addition to extra-glomerular basement membranes and extracellular matrix. All antibodies also stained cellular outgrowths of isolated glomeruli cultured in vitro, and showed additive binding to cultured cells by radioimmunoassay. Physical characterization using absorptions with purified substrates, plus specific chemical and enzymatic digestions, indicated that PHM12 is directed against type IV collagen. PHM13 is directed against fibronectin as shown by absorption with purified fibronectin and immunoprecipitation of a 220 000 MW glycoprotein. The remaining 5 monoclonal antibodies, which react with carbohydrate (PHM7) or protein (PHM8-PHM11) determinants, were shown to be nonreactive with type IV collagen, fibronectin or other known glomerular components including sialic acid, laminin, amyloid P-component or various glycosaminoglycans. These monoclonal antibodies therefore appear to define a new series of human glomerular antigens, or possibly closely related antigenic determinants, which are synthesized by glomerular cells and incorporated into the mesangium and glomerular basement membrane. These antibodies, by providing markers for at least 2 antigens known to be important in glomerular cell-matrix interactions, should prove useful in research into the mechanisms involved in renal pathology.

Immunohistological studies indicate that T cells and macrophages are the major components of human kidney allograft infiltrates. Recent work has demonstrated a division of T lymphocytes into 2 subpopulations with distinct functions on the basis of their expression of the CD45R antigen (CD45R+ "naive" and CD45R- "memory" T cells). This study analyzes CD45R expression on circulating T cells and T cells infiltrating renal allografts in patients undergoing rejection and/or cyclosporine nephrotoxicity. The percentage of circulating T cells that expressed CD45R in patients with rejecting (63 +/- 4) or stable grafts (66 +/- 3) was not different from values obtained for normal donors (62 +/- 3). In contrast, the percentage of T cells expressing CD45R infiltrating rejecting grafts was 21 +/- 2 and was not affected by the stage of rejection; in patients with CsA toxicity the value was 22 +/- 6. The reduced proportion of T cells that expressed CD45R in the allograft may reflect a change in status from the naive state due to alloantigenic stimulation (which can be demonstrated in vitro) and/or a propensity of memory T cells to enter or be retained in an allograft.