Recombinant human IL-16 inhibits HIV-1 replication and protects against activation-induced cell death (AICD)

The chemoattractant cytokine IL-16 has been reported to suppress lymphocyte activation and to inhibit HIV-1 replication in acutely infected T cells. We have cloned and expressed human IL-16 in Escherichia coli and investigated whether the recombinant protein could regulate the level of lymphocyte apoptosis from HIV-1-infected subjects. After purification and refolding, only 2–10% of the recombinant cytokine was present in a biologically active homotetrameric form. This could explain the need for high concentrations of the bacterially derived IL-16 to induce significant inhibition of HIV-1 replication. Addition of IL-16 to unstimulated peripheral blood mononuclear cell (PBMC) cultures from HIV-1-infected subjects did not modify the observed level of spontaneous lymphocyte apoptosis. In contrast, IL-16 added to PBMC cultures stimulated with anti-CD3, anti-CD95 or dexamethasone reduced significantly the percentage of lymphocytes undergoing AICD. This effect was found to correlate with the ability of the cytokine to decrease CD95 expression on activated CD4⁺ T cells. Comparative studies on PBMC from healthy individuals indicated that the regulation of apoptosis levels by IL-16 is a complex phenomenon and could depend on the nature of the activator used and/or the immune status of lymphocytes tested. The outcome of CD4 cross-linking on T cells by various ligands is discussed in the context of the observed beneficial activities of IL-16 and its potential role in the treatment of HIV disease.     

SS-56, a novel cellular target of autoantibody responses in Sjögren syndrome and systemic lupus erythematosus

Certain autoimmune disorders, including Sj?gren syndrome (SS) and systemic lupus erythematosus (SLE), are characterized by autoantibodies against the Ro/SSA and La/SSB cellular antigens. Although the implication of these autoantibodies in disease pathogenesis is still unclear, it is believed that the aberrant responses against autoantigens may extend to other proteins that are not yet well defined. In an attempt to analyze the regulated gene expression in lymphocytes by an HIV-suppressive immunomodulator, we have identified and cloned a novel gene encoding a 56-kDa protein, named SS-56, which is structurally related to the 52-kDa Ro/SSA antigen. The new protein showed primarily perinuclear cytoplasmic localization, and recombinant SS-56 was found to react in ELISA with sera from most patients with SS or SLE. Western blot analysis confirmed the autoantigenic nature of native SS-56 in extracts from HeLa cells. Interestingly, the incidence of antibodies to SS-56 was associated with visceral complications in SLE, and roughly half of the 17 SS or SLE patients with no detectable antibodies to SSA and SSB antigens presented measurable antibodies against recombinant SS-56. Thus, SS-56 represents a new member of the SS family of autoantigens and could become an additional and important diagnostic marker for SS and SLE.     

Interleukin-18 modulates immune responses induced by HIV-1 Nef DNA prime/protein boost vaccine

Many different HIV-1 vaccine strategies have been developed, but as yet none has been completely successful. Promising results from combined DNA prime/protein boost vaccines have been reported. Specific immune responses generated by DNA vaccines can be modulated by the co-delivery of genes coding for cytokines. In this study, we have used the intradermal route by needle injection of a plasmid coding for the HIV-1 Nef accessory protein. We show that DNA prime/protein boost vaccine combinations increase the humoral and cellular immune responses against HIV-1 Nef and that the co-injection of DNA encoding Interleukin-18 (IL-18) modulates the specific immune response towards a Th1 type.     

Modulation of cellular and humoral immune responses to a multiepitopic HIV-1 DNA vaccine by interleukin-18 DNA immunization/viral protein boost

In this study, the impact of Th1-inducing cytokine gene co-delivery and antigen boosting on humoral and cellular responses induced by multiepitopic DNA immunization in mice have been investigated. Intramuscular injection of mixed DNA constructs encoding for HIV-1 Gag, Tat and Nef proteins, co-administered with the DNA encoding for interleukin-18 (IL-18) have been used. The effect of boosting with the recombinant proteins was also evaluated on the outcome of the responses in DNA-primed mice. It was demonstrated that at least two DNA immunizations were necessary to generate virus specific Th-1 responses detected by the presence of cytotoxic T lymphocyte (CTL) and by the secretion of IL-2 and IFN-gamma, but not IL-4 and IL-10, in antigen-stimulated splenocyte cultures. Interestingly, co-delivery of Th-1-inducing IL-18 gene was able to shorten by 2 weeks, the CTL induction time, and to increase the antigen-induced secretion of IL-2 and IFN-gamma. Furthermore, IL-18 co-delivery enhanced antigen-specific lymphoproliferative responses, and this was most evident in mice that were primed and boosted with plasmid DNA. However, the induction of detectable antibodies in mice required two DNA vaccinations and a protein boost. In contrast to the effects on cell-mediated immunity, co-administration of IL-18-plasmid resulted in decreased antibody titers against viral proteins.