Oriented display of HIV-1 Env trimers by a novel coupling strategy enhances B cell activation and phagocytosis.

Introduction: Conformationally stabilized Env trimers have been developed as antigens for the induction of neutralizing antibodies against HIV-1. However, the non-glycosylated immunodominant base of these soluble antigens may compete with the neutralizing antibody response. This has prompted attempts to couple Env trimers to organic or inorganic nanoparticles with the base facing towards the carrier. Such a site-directed coupling could not only occlude the base of the trimer, but also enhance B cell activation by repetitive display. Methods: To explore the effect of an ordered display of HIV-1 Env on microspheres on the activation of Env-specific B cells we used Bind&Bite, a novel covalent coupling approach for conformationally sensitive antigens based on heterodimeric coiled-coil peptides. By engineering a trimeric HIV-1 Env protein with a basic 21-aa peptide (Peptide K) extension at the C-terminus, we were able to covalently biotinylate the antigen in a site-directed fashion using an acidic complementary peptide (Peptide E) bearing a reactive site and a biotin molecule. This allowed us to load our antigen onto streptavidin beads in an oriented manner. Results: Microspheres coated with HIV-1 Env through our Bind&Bite system showed i) enhanced binding by conformational anti-HIV Env broadly neutralizing antibodies (bNAbs), ii) reduced binding activity by antibodies directed towards the base of Env, iii) higher Env-specific B cell activation, and iv) were taken-up more efficiently after opsonization compared to beads presenting HIV-1 Env in an undirected orientation. Discussion: In comparison to site-directed biotinylation via the Avi-tag, Bind&Bite, offers greater flexibility with regard to alternative covalent protein modifications, allowing selective modification of multiple proteins via orthogonal coiled-coil peptide pairs. Thus, the Bind&Bite coupling approach via peptide K and peptide E described in this study offers a valuable tool for nanoparticle vaccine design where surface conjugation of correctly folded antigens is required.

Activation of murine lymphocytes and modulation of macrophage functions by fractions of Alchornea cordifolia (Euphorbiaceae) leaf extract.

The immune system is highly complex, intricately regulated group of cells whose integrated function is essential to health. Modulating the functions of these cells offers important pharmacological and therapeutic approaches in many disease conditions.This study reports on the in vitro immunostimulant activities of two flavonoid-rich fractions of Alchornea cordifolia (Euphorbiaceae) leaf extract: EAC and AAC, obtained by fractionating the methanol extract into ethylacetate and acetone soluble fractions, respectively.The lymphoproliferative effect of the fractions on naïve murine splenocytes and thymocytes as well as the modulatory effects on the phagocytic and lysosomal enzyme activities of elicited murine macrophages was investigated. A. cordifolia fractions, EAC and AAC, produced significant (P<0.05) and concentration-related (10-250 microg/ml) increases in the proliferation of splenocytes and thymocytes cultures which were comparable to the mitogenic effects of lipopolysaccharide, LPS (10 microg/ml) and concanavalin A, ConA (2 microg/ml) used as standard mitogens. EAC and AAC (15.6-250 microg/ml) significantly (P<0.05) increased phagocytosis and intracellular killing capacity measured as percentage increase in nitroblue tetrazolium (NBT) dye reduction. Lysosomal phosphatase activity of peritoneal macrophages, measured by p-nitrophenyl phosphate (p-NPP) hydrolysis, was also increased significantly (P<0.05) by EAC and AAC (15.6-250 microg/ml). Treatment of macrophage cultures with EAC and AAC (15.6-250 microg/ml) decreased the expression of nitric oxide significantly (P<0.05) in the supernatant. This study demonstrates strong immunomodulatory activities of A. cordifolia leaf extracts which could explain some of the therapeutic benefits attributed to the plant in traditional medicine and could also be exploited as a source of novel immunoregulating substances.