Inhibition of HIV-1 by modification of a host membrane protease

While it is clear that CD4 Is the receptor for the gp120 envelopeprotein of HIV-1, substantial evidence suggests that other hostcell proteins are required for successful membrane fusion. Studieswere initiated to examine the potential for a protein receptorwhich has an elastase-like character to participate in fusionof HIV-1 with permissive host cells. A synthetic elastase inhibitorwas shown to significantly reduce HIV-1 infectivity when presentduring, but not after, the initial contact between virus andcells. A human T cell elastase-like membrane component was purifiedand shown to be lipid-associated. By competitive Inhibition,the purified protein was shown to bind gp160 within the HIV-1fusion domain. The binding parameters of whole T cell membraneextract, with a hydrophobic pentapeptide representative of thefusion domain, suggested an elastase-like protein is the single,secondary T cell receptor for HIV-1 (K = 1x10³ M^–1). Thepentapeptide interacted with porcine and human (epithelial andpolymorphonuclear leukocyte), but not murine, elastase isoforms,suggesting its participation In the permissiveness of host cellsto infection.     

Mechanism(s) promoting HIV-1 infection of primary unstimulated T lymphocytes in autologous B cell/T cell co-cultures

Resting CD4(+) T cells in the lymphoid tissue (LT) are essential producers of virions at the beginning of HIV infection in vivo. We previously developed a model that allowed in vitro infection of non-prestimulated T lymphocytes in the presence of autologous B lymphocytes and complement. In this study, we try to clarify the mechanism(s) responsible for virus transmission in unstimulated autologous B cell/T cell co-cultures. Ex vivo analyses of patient plasma samples revealed that HIV was opsonized. Flow cytometry showed that opsonized virus preferentially bound to complement receptor (CR)-2 on B lymphocytes in primary B cell/T cell co-cultures. As indicated by cytokine measurements and transwell experiments, soluble factors seemed to play a minor role in enabling infection. Rather, direct interaction between B and T lymphocytes and direct binding of opsonized virus to CR2 on B cells turned out to be essential for productive infection. Antibodies blocking cell-cell adhesion inhibited p24 antigen production. An anti-CR2 antibody blocking C3d-CR2 binding also significantly reduced viral replication. Since the infection of unstimulated T cells by opsonized primary HIV isolates in the presence of B cells was highly efficient independent of the tropism of the virus, this mechanism may be critical in the pathogenesis of HIV.     

Changes in lymphocyte chromatin in Down's syndrome revealed by the thermal denaturation method

A luminescence-microscopic study using acridine orange with a short-term culture of human cells showed that DNA melting profiles of the chromatin of intact lymphocytes of healthy donors are curves with maxima (F 530) in the temperature regions of 45, 65, 78, 85, 88, and 92°C (P<0.01). The melting profiles of lymphocytes of patients with Down's syndrome are curves with maxima in the temperature regions of 65, 85, 88, and 92°C (P<0.01). The absence of a decrease in the intensity of fluorescence between 78 and 85°C is evidently due to the greater degree of condensation of certain regions of the chromatin complex of the trisomic cells. The possible mechanisms of the structural changes in the interphase chromatin, of human lymphocytes under the influence of temperature are discussed.Institute of Medical Genetics, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR N. A. Yudaev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 6, pp. 672–674, June, 1976.     

Alteration in plasma glucose levels in Japanese encephalitis patients

A unique factor, human T cell hypoglycaemic factor (hTCHF), has been shown to produce hypoglycaemia during the convalescent stage in the plasma of patients with Japanese encephalitis virus (JEV) infection. The present study was undertaken to investigate the ability of T cells from fresh peripheral blood mononuclear cells (PBMC) of such patients to produce hTCHF. The PBMC, as well as the individual subpopulations, were cultured for 24 h and the culture supernatants (CS) were assayed for hypoglycaemic activity. The activity was observed in the CD8+ T cells. The hypoglycaemia in JE-confirmed patients coincided with the gradual rise in circulating glucagon level, with no significant alterations in insulin, growth hormone and cortisol levels. The hTCHF was purified by ion exchange chromatography and the purified protein was observed as a approximately 25 kDa band on SDS-PAGE. Secretory hTCHF in the sera of patients and T cell CS was present in 88% of convalescent serum samples. We conclude that during the convalescent stage of JEV infection, a unique factor, hTCHF, is secreted by activated CD8+ T cells from patients and that this is responsible for the development of hypoglycaemia.     

Serological distinction of integral plasma membrane proteins as a class of mycobacterial antigens and their relevance for human T cell activation

This study pertains to classification and antigenic analysis of mycobacterial plasma membrane proteins in relation to human T cell proliferative responses, using a ‘fast grower’ Mycobacterium fortuitum as model. Membrane vesicles, prepared by sonication and differential centrifugation, were subjected to biphasic Triton X-1 14 extraction for isolation of integral (detergent phase) and peripheral (aqueous phase) proteins. Neither protein pool showed any appreciable overlap serologically. SDS-PAGE showed five prominent bands in peripheral and three in the integral protein pool, whereas immunoblotting with rabbit antisera identified only two major antigens (60 and 67kD) in the former and five (24, 34, 42, 51 and 54kD) in the latter, ELISA with a panel of anti-mycobacterial MoAbs revealed that nine out of 12 previously known antigens were present in the peripheral protein pool. Only two of them (33 and 40 kD) were additionally detected amongst integral proteins. The membrane-associated immunosuppressive moiety lipoarabinomannan was semiquantitatively located in aqueous phase. In bulk T cell proliferation assays, seven out of 10 subjects belonging to a ‘responder’ background (BT-BB leprosy patients and healthy contacts) showed high responses for Myco. fortuitum antigens. Proliferative response with integral proteins was comparable to that with whole membrane, hut it was significantly higher (P < 0.0005) than t he response with peripheral proteins. The distinction and relevance of integral membrane proteins as a class of mycobacterial antigens make them worthy of consideration in a subunit vaccine design.     

Heligmosomoides polygyrus inhibits established colitis in IL-10-deficient mice

Inflammatory bowel disease (IBD) is prevalent in industrialized countries, but rare in less-developed countries. Helminths, common in less-developed countries, may induce immunoregulatory circuits protective against IBD. IL-10(-/-) mice given piroxicam develop severe and persistent colitis. Lamina propria mononuclear cells from colitic IL-10(-/-) mice released IFN-gamma and IL-12. The ongoing piroxicam-induced colitis could be partially blocked with anti-IL-12 monoclonal antibody suggesting that the inflammation was at least partly IL-12 dependent. Colonization of piroxicam-treated colitic IL-10(-/-) mice with Heligmosomoides polygyrus (an intestinal helminth) suppressed established inflammation and inhibited mucosal IL-12 and IFN-gamma production. H. polygyrus augmented mucosal IL-13, but not IL-4 or IL-5 production. Transfer of mesenteric lymph node (MLN) T cells from IL-10(-/-) animals harboring H. polygyrus into colitic IL-10(-/-) recipients inhibited colitis. MLN T cells from worm-free mice did not. Foxp3 (scurfin) drives regulatory T cell function. H. polygyrus enhanced Foxp3 mRNA expression in MLN T cells that had regulatory activity. This suggests that H. polygyrus inhibits ongoing IL-10(-/-) colitis in part through blocking mucosal Th1 cytokine production. Resolution of inflammation is associated with increased IL-13 production and can be adoptively transferred by MLN T cells.