Molecular characterization of feline interleukin 16: chemotactic activity and effect on feline immunodeficiency virus infection and/or replication

Identification and characterization of pro-interleukin-16 from mud crab Scylla paramamosain: The first evidence of proinflammatory cytokine in crab species

IL-16 is a pro-inflammatory cytokine originally designated as a lymphocyte chemoattractant factor. In mammal and avian, it has been characterized as an essential regulator of various cellular processes including cell recruitment and activation against pathogen invasion. So far, neither of the full-length of IL-16 homologue nor the response mechanism against pathogen was reported in crab species. In the present study, the pro-IL-16 homologue was firstly cloned and characterized from mud crab Scylla paramamosain. The full-length Sp-pro-IL-16 consisted of 4107 bp with an opening reading frame encoding 1369 amino acids. Multiple alignment analysis showed the putative amino acid sequence of Sp-pro-IL-16 had about 73.86% identity with Litopenaeus vannamei pro-IL-16. Additionally, two conserved PDZ domains and protein binding sites were found in Sp-pro-IL-16 and showed high similarities about 94.19% and 51.14% with their Litopenaeus vannamei and Mus musculus counterparts. RT-PCR analysis indicated that Sp-pro-IL-16 transcripts were constitutively expressed in all tissues examined with an extreme high level in hepatopancreas. Moreover, Sp-pro-IL-16 transcripts in hepatopancreas were significantly up-regulated 15-fold at 72 h after Vibrio alginolyticus challenge and 3.5-fold at 12 h after virus-analog Poly (I:C) challenge. The Western blot analysis revealed that Sp-pro-IL-16 can be cleaved to its bioactive form, an approximately 35 kDa mature IL-16, and the protein levels of both pro-IL-16 and mature IL-16 increased after Vibrio alginolyticus challenge. It is the first experimental identification of pro-inflammatory cytokine IL-16 in arthropods. This study could shed new light on further understanding of the response mechanism of pro-inflammatory cytokine IL-16 in Scylla paramamosain against pathogens. Meanwhile, it brought new insight into the origin and evolution of IL-16 in crab species.

Immunomodulation of caprine lentiviral infection by interleukin-16

Interleukin-16 (IL-16) is a proinflammatory cytokine produced by a variety of cells including lymphocytes, macrophages, mast cells, and eosinophils. We have shown in our previous studies increased expression of IL-16 mRNA and protein in caprine arthritis-encephalitis virus (CAEV)-infected goats blood. In this study, we determined the immunomodulatory effects of IL-16 in vitro using cells derived from CAEV infected and uninfected goats. Human recombinant IL-16 (rhIL-16) significantly increased chemotaxis of peripheral blood mononuclear cells (PBMCs) of both control and CAEV-infected goats. Pretreatment of PBMC with anti-goat CD4 monoclonal antibody inhibited IL-16-induced chemotaxis of PBMC of control and infected goats suggesting that IL-16 exerts its action in goats primarily by binding to CD4. The CAEV proviral DNA was less in caprine monocytes treated with rhIL-16 infected in vitro with CAEV. These data suggest inhibitory effect of IL-16 on viral integration. Flow cytometric studies indicated a trend toward IL-16-induced increased expression of lymphocyte activation markers. Combined with our previously reported data, these experiments suggest that increased IL-16 expression during CAEV infection may inhibit viral integration.

FIV as a Model for HIV: An Overview

Animal models for human immunodeficiency virus (HIV) infection play a key role in understanding the pathogenesis of AIDS and the development of therapeutic agents and vaccines. As the only lentivirus that causes an immunodeficiency resembling that of HIV infection, in its natural host, feline immunodeficiency virus (FIV) has been a unique and powerful model for AIDS research. FIV was first described in 1987 by Niels Pedersen and co-workers as the causative agent for a fatal immunodeficiency syndrome observed in cats housed in a cattery in Petaluma, California. Since this landmark observation, multiple studies have shown that natural and experimental infection of cats with biological isolates of FIV produces an AIDS syndrome very similar in pathogenesis to that observed for human AIDS. FIV infection induces an acute viremia associated with Tcell alterations including depressed CD4 :CD8 T-cell ratios and CD4 T-cell depletion, peripheral lymphadenopathy, and neutropenia. In later stages of FIV infection, the host suffers from chronic persistent infections that are typically self-limiting in an immunocompetent host, as well as opportunistic infections, chronic diarrhea and wasting, blood dyscracias, significant CD4 T-cell depletion, neurologic disorders, and B-cell lymphomas. Importantly, chronic FIV infection induces a progressive lymphoid and CD4 T-cell depletion in the infected cat. The primary mode of natural FIV transmission appears to be blood-borne facilitated by fighting and biting. However, experimental infection through transmucosal routes (rectal and vaginal mucosa and perinatal) have been well documented for specific FIV isolates. Accordingly, FIV disease pathogenesis exhibits striking similarities to that described for HIV-1 infection.

Prospects for IL-16 in the treatment of AIDS

IL-16 is a multi-functional cytokine that uses CD4 as a receptor to signal diverse biological activities by target cells including T-lymphocytes, monocytes and eosinophils. IL-16 has been shown to repress HIV-1 infection in lymphocytes and monocytic cells and it is active against both laboratory and naturally acquired virus isolates. In lymphocytes, the repressive effect of IL-16 occurs at the level of virus transcription, while it appears to inhibit viral entry in monocytic cells. Clinical studies comparing serum IL-16 levels with the state of HIV-1 disease suggest that this cytokine is a functionally significant endogenous antiviral factor. The antiviral activity of IL-16 may be of therapeutic benefit in HIV/AIDS but its greatest potential is for immune reconstitution. Stimulation of CD4+ T-cells with IL-16 primes cells to respond to IL-2, by upregulating the expression of IL-2 receptor p75 (CD25). Co-treatment of peripheral blood mononuclear cells (PBMC) with IL-16 plus IL-2 (or IL-15) in vitro selectively expands the population of CD4+ T-cells. Clinical trials of recombinant IL-2 have already shown promise in HIV/AIDS. In combination with IL-16, the beneficial effects of IL-2 may be augmented and specifically targeted to CD4+ T-cells. Thus, IL-16 shows considerable promise as an agent for the biological therapy of HIV/AIDS.

Immunization of cats against feline immunodeficiency virus (FIV) infection by using minimalistic immunogenic defined gene expression vector vaccines expressing FIV gp140 alone or with feline interleukin-12 (IL-12), IL-16, or a CpG motif

Four groups of cats, each containing four animals, were immunized at 0, 3, and 6 weeks with minimalistic immunogenic defined gene expression vector (MIDGE) vaccines containing the gene(s) for feline immunodeficiency virus (FIV) gp140, FIV gp140 and feline interleukin-12 (IL-12), FIV gp140 and feline IL-16, or FIV gp140 and a CpG motif. MIDGEs were coated onto gold beads and injected intradermally with a gene gun. A fifth group of four cats were immunized in an identical manner but with blank gold beads. All cats were challenge exposed to virulent FIV 4 weeks following the final immunization, and the course of infection was monitored. The two groups of cats immunized with the FIV gp140 gene alone or with blank gold particles became highly viremic and seroconverted as early as 4 weeks after infection. In contrast, three of four cats immunized with FIV gp140 in combination with feline IL-12 failed to become viremic or seropositive, as has been shown elsewhere (F. S. Boretti, C. M. Leutenegger, C. Mislin, et al., AIDS 14:1749-1757, 2000). Here we show the effect of IL-12 when used as an adjuvant on the viral RNA and DNA load and on the cytokine profile. In addition, the two groups of cats immunized either with gp140 and IL-16 or with gp140 and the CpG had greatly reduced viremia. Protection correlated weakly with cytotoxic T-lymphocyte activity and increased cytokine transcription of IL-12, gamma interferon, and IL-10 by peripheral blood mononuclear cells in the postchallenge period. This study extends the data on IL-12 and provides new results on CpG motifs and IL-16 used as adjuvants in the FIV cat model.

Vaccination with feline immunodeficiency virus induces CD4 epitope masking by soluble factors

Soluble factors are important effector mechanisms to control for lentiviral replication. Vaccination of cats with recombinant outer surface proteins (SU) of the FIV envelope protein in combination with complete Freund adjuvant (CFA) and rabies nucleocapsid (NC) protein led to significantly reduced viral loads [Leutenegger, C.M., Hofmann-Lehmann, R., Holznagel, E., Cuisinier, A.M., Wolfensberger, C., Duquesne, V., Cronier, J., Allenspach, K., Aubert, A., Ossent, P. , Lutz, H., 1998. AIDS Res. Hum. Retroviruses, 14(3) 275-283]. Lymphocytes from vaccinated and non-vaccinated cats were stained with two monoclonal antibodies, Fel7 and CAT30A, directed against the feline CD4 antigen. Peripheral blood lymphocytes from cats vaccinated with the SU glycoprotein, CFA and rabies NC protein showed a significantly reduced number of cells after staining with CAT30A, while the number in Fel7 positive lymphocytes remained unchanged. This decreased CAT30A fluorescent staining could be reproduced in vitro by pre-incubating FIV-negative lymphocytes with immune sera from cats in which reduced CAT30A staining was detected. Neither experimental infection nor vaccination with the unglycosylated SU protein alone resulted in this epitope masking. Furthermore, this masking phenomenon was negatively correlated with a decreased susceptibility to activation-induced cell death (AICD). These findings will be discussed based on the current knowledge of CD8(+) T-cell antiviral factors and their involvement in lentiviral infection and/or replication.