Dendritic cells (DCs) are important targets for human immunodeficiency virus (HIV) because of their roles during transmission and also maintenance of immune competence. Furthermore, DCs are a key cell in the development of HIV vaccines. In both these settings the mechanism of binding of the HIV envelope protein gp120 to DCs is of importance. Recently a single C-type lectin receptor (CLR), DC-SIGN, has been reported to be the predominant receptor on monocyte-derived DCs (MDDCs) rather than CD4. In this study a novel biotinylated gp120 assay was used to determine whether CLR or CD4 were predominant receptors on MDDCs and ex vivo blood DCs. CLR bound more than 80% of gp120 on MDDCs, with residual binding attributable to CD4, reconfirming that CLRs were the major receptors for gp120 on MDDCs. However, in contrast to recent reports, gp120 binding to at least 3 CLRs was observed: DC-SIGN, mannose receptor, and unidentified trypsin resistant CLR(s) . IntroductionDendritic cells (DCs) play a major role in human immunodeficiency virus (HIV) pathogenesis. Peripheral or surveillance mucosal DCs are one of the first cell types infected and are distributed in the vaginal, ectocervical, and anal mucosa, 1,2 allowing contact with HIV during mucosal exposure. Thus, after vaginal inoculation with simian immunodeficiency virus in macaques, DCs are the predominant cell type infected. 3 Furthermore, the ability of DCs to cluster with and stimulate T cells may also play a key role in establishing infection. DCs from skin, mucosa, and blood of humans and macaques can participate in highly productive HIV and simian immunodeficiency virus infection in DC-T-cell cocultures and illustrates the importance of this natural DC-T-cell synergy. [4][5][6][7] Key aspects of HIV binding to DC via gp120 are ill-defined, particularly to the different types of DCs. CD11c ϩve and CD11c Ϫve blood DCs, Langerhans cells (LCs), and in vitro-derived monocytederived DCs (MDDCs) all express CD4 and CCR5 and can be productively infected in vitro. [8][9][10][11][12] However, HIV also bound several DC populations independently of CD4. 8,13,14 The heavy glycosylation of gp120 with mannose and fucose saccharides suggested HIV bound to cells also via lectin receptors. Binding of gp120 to a novel C-type lectin receptor (CLR), originally identified from a placental complementary DNA (cDNA) library 15 on the basis of HIV gp120 binding and named clone 11, on MDDCs was recently reported. 14,16 The adhesion properties of this CLR were also defined and the receptor subsequently renamed DC-SIGN (dendritic cell specific ICAM-3 grabbing nonintegrin). Although MDDCs express a diverse and abundant array of CLRs in addition to DC-SIGN, [16][17][18][19][20][21][22][23][24] and given substantial overlap in saccharide recognition by such CLRs, they may also serve as receptors for gp120 on MDDCs. The roles of CD4 and CLRs on most other in vivo DC types are unknown.This study aimed to define the contributions of CD4 and CLRs in binding gp120, to address and identify the capacity o...

Factor XIII is a blood protransglutaminase that is distributed in plasma and platelets. The extracellular and intracellular zymogenic forms differ in that the plasma zymogen contains A and B subunits, while the platelet zymogen has A subunits only. Both zymogens form the same enzyme. Erythrocytes, in contrast, contain a tissue transglutaminase that is distinct from Factor XIII. In this study other bone marrow-derived cells were examined for transglutaminase activity. Criteria that were used to differentiate Factor XIII proteins from erythrocyte transglutaminase included: (a) immunochemical and immunohistochemical identification with monospecific polyclonal and monoclonal antibodies to Factor XIII proteins, (b) requirement for thrombin cleavage to express activity, (c) pattern of fibrin cross-linking catalyzed by the enzyme, and (d) different electrophoretic mobilities in nondenaturing gel systems. By these criteria human peripheral blood monocytes, peritoneal macrophages, and monocytes maintained in culture contain an intracellular protransglutaminase that is the same as platelet Factor XIII. The monocyte-macrophage protein is thrombin-sensitive, and under appropriate conditions there is no enzyme expression without activation of the zymogen. Both the monocyte-macrophage zymogen and enzyme have the same electrophoretic mobilities as platelet Factor XIII zymogen and enzyme. Antibody to A protein reacts with the monocyte-macrophage protein. B protein is not associated with this intracellular zymogen. By immunoperoxidase staining monocyte-macrophage protein seems to be localized in the cytoplasm, similar to the known cytoplasmic distribution of platelet and megakaryocyte Factor XIII. These procedures were also used to study populations of human granulocytes and lymphocytes, and protransglutaminase activity was not observed in these cells.

The chemokine receptor CCR5 and to a lesser extent CCR3 and CCR2b have been shown to serve as coreceptors for human immunodeficiency virus type 1 (HIV-1) entry into blood- or tissue-derived macrophages. Therefore, we examined the expression of the chemokine receptors CCR1, CCR2b, CCR3, CCR5, and CXCR4 as RNAs or as membrane-expressed antigens in monocytes maturing into macrophages and correlated these results with the susceptibility of macrophages to HIV-1 infection, as measured by their concentrations of extracellular p24 antigen and levels of intracellular HIV DNA by quantitative PCR. There was little change in levels of CCR1, CCR2b, and CCR5 RNAs. CCR3 RNA and surface antigen were undetectable throughout maturation of adherent monocytes over 10 days. CXCR4 RNA and membrane antigen were strongly expressed in newly adherent monocytes, but their levels declined at day 7. The amounts of CCR5 RNA remained stable, but the amounts of CCR5 antigen increased from undetectable to peak levels at day 7 and then declined slightly at day 10. Levels of susceptibility to laboratory (HIV-1BaL) and clinical strains of HIV-1 showed parallel kinetics, peaking at day 7 and then decreasing at days 10 to 14. The concordance of levels of HIV DNA and p24 antigen suggested that the changes in susceptibility with monocyte maturation were at or immediately after entry and correlated well with CCR5 expression and inversely with CXCR4 expression.