Acute and chronic effects of nicotine on the immune system are usually opposite; acute treatment stimulates while chronic nicotine suppresses immune and inflammatory responses. Nicotine acutely raises intracellular calcium ([Ca2+]i) in T cells, but the mechanism of this response is unclear. Nicotinic acetylcholine receptors (nAChRs) are present on neuronal and non-neuronal cells, but while in neurons, nAChRs are cation channels that participate in neurotransmission; their structure and function in nonexcitable cells are not well-defined. In this communication, we present evidence that T cells express α7-nAChRs that are critical in increasing [Ca2+]i in response to nicotine. Cloning and sequencing of the receptor from human T cells showed a full-length transcript essentially identical to the neuronal α7-nAChR subunit (>99.6% homology). These receptors are up-regulated and tyrosine phosphorylated by treatment with nicotine, anti-TCR Abs, or Con A. Furthermore, knockdown of the α7-nAChR subunit mRNA by RNA interference reduced the nicotine-induced Ca2+ response, but unlike the neuronal receptor, α-bungarotoxin and methyllycaconitine not only failed to block, but also actually raised [Ca2+]i in T cells. The nicotine-induced release of Ca2+ from intracellular stores in T cells did not require extracellular Ca2+, but, similar to the TCR-mediated Ca2+ response, required activation of protein tyrosine kinases, a functional TCR/CD3 complex, and leukocyte-specific tyrosine kinase. Moreover, CD3ζ and α7-nAChR coimmunoprecipitated with anti-CD3ζ or anti-α7-nAChR Abs. These results suggest that in T cells, α7-nAChR, despite its close sequence homology with neuronal α7-nAChR, fails to form a ligand-gated Ca2+ channel, and that the nicotine-induced rise in [Ca2+]i in T cells requires functional TCR/CD3 and leukocyte-specific tyrosine kinase.

The simian immunodeficiency viruses (SIV) naturally infect a wide range of African primates, includingAfrican green monkeys (AGM). Despite moderate to high levels of plasma viremia in naturally infected AGM, infection is not associated with immunodeficiency. We recently reported that SIVagmVer90 isolated from a naturally infected vervet AGM induced AIDS following experimental inoculation of pigtailed macaques. The goal of the present study was to evaluate the replication of this isolate in two species of AGM, sabaeus monkeys (Chlorocebus sabaeus) and vervets (C. pygerythrus). Inoculation of sabaeus AGM with SIVagmVer90 resulted in low and variable primary and set-point viremia (<10 2 to 10 4 copies/ml). In contrast, inoculation of vervet AGM with either SIVagmVer90 or blood from a naturally infected vervet (Ver1) resulted in high primary viremia and moderate plateau levels, similar to the range seen in naturally infected vervets from this cohort. CD4 ؉ T cells remained stable throughout infection, even in AGM with persistent high viremia. Despite the lack of measurable lymphadenopathy, infection was associated with an increased number of Ki-67 ؉ T cells in lymph node biopsies, consistent with an early antiviral immune response. The preferential replication of SIVagmVer in vervet versus sabaeus AGM shows that it is critical to match AGM species and SIV strains for experimental models of natural SIV infection.

As a simian species, the langurs are not known to harbor simian retroviruses, except for one report on a simian Type D endogenous retrovirus from the spectacled langur (Trachypithecus obscurus) from Malaysia. The present report describes for the first time natural infection of the common Hanuman langur (Semnopithecus entellus) from India by a novel simian retrovirus (SRV). The new SRV is phylogenetically related to but distinct from the three molecularly characterized serotypes, SRV 1-3, of the five known serotypes of SRVs, based on sequence analyses from the 3'orf and env regions of the viral genome. The novel SRV isolated from the Indian Hanuman langur is provisionally named SRV-6.

Natural infection of feral Indian rhesus monkeys (Macaca mulatta) by a new simian beta retrovirus, provisionally called simian retrovirus-7 (SRV-7) is described. The virus is capable of in vitro replication in primary human peripheral blood lymphocytes (PBL) and B and T cell lines. We have earlier reported a novel SRV, SRV-6 from Indian langurs (Semnopithecus entellus). Additional sequence analyses from gp20 transmembrane (TM) env genes of SRV-6 and SRV-7 place them in a separate cluster, related to but distinct from known exogenous SRVs and also close to the simian endogenous beta retrovirus, (SERV) from African baboon. Phylogenetic analyses of pol gene of SRV-7 place it closer to SERV when the stop codons of the SERV genes are removed. On the other hand, additional sequence data from gp70, surface glycoprotein (SU) region of the env gene of SRV-6 suggest it is more closely related to known exogenous SRVs, (SRV-1 to 3). It is also related to the endogenous langur virus, Po-1-Lu. We hypothesize that SRV-6 and SRV-7 probably originated from a progenitor exogenous SRV which recombined with an endogenous SERV in the TM env and pol genes during evolution, based on the phylogenetic analyses.