HIV infection in vitro enhances the activity of src-family protein tyrosine kinases

New targets for HIV drug discovery

Recent estimates suggest close to one million people per year die globally owing to HIV-related illnesses. Therefore, there is still a need to identify new targets to develop future treatments. Many of the more recently identified targets are host-related and these might be more difficult for the virus to develop drug resistance to. In addition, there are virus-related targets (capsid and RNAse H) that have yet to be exploited clinically. Several of the newer targets also address virulence factors, virus latency or target persistence. The targets highlighted in this review could represent the next generation of viable candidates for drug discovery projects as well as continue the search for a cure for this disease.

c-SRC protein tyrosine kinase regulates early HIV-1 infection post-entry

OBJECTIVE

We investigated whether HIV-1 inhibition by SRC-family kinase inhibitors is through the non-receptor tyrosine kinase pp60 (c-SRC) and its binding partner, protein tyrosine kinase 2 beta (PTK2B).

DESIGN

CD4 T-lymphocytes were infected with R5 (JR-FL) or X4 (HXB2) HIV-1. We used SRC-family kinase inhibitors or targeted siRNA knockdown of c-SRC and PTK2B, then monitored effects on the early HIV-1 lifecycle.

METHODS

Four SRC-family kinase inhibitors or targeted siRNA knockdown were used to reduce c-SRC or PTK2B protein expression. Activated CD4 T-lymphocytes were infected with recombinant, nef-deficient, or replication-competent infectious viruses. Knockdown experiments examined early infection by monitoring: luciferase activity, expression of host surface receptors, reverse transcriptase activity, p24 levels and qPCR of reverse transcripts, integrated HIV-1, and two-long terminal repeat (2-LTR) circles.

RESULTS

All SRC-family kinase inhibitors inhibited R5 and X4 HIV-1 infection. Neither c-SRC nor PTK2B siRNA knockdown had an effect on cell surface receptors (CD4, CXCR4, and CCR5) nor on reverse transcriptase activity. However, using JR-FL both decreased luciferase activity while increasing late reverse transcripts (16-fold) and 2-LTR circles (eight-fold) while also decreasing viral integration (four-fold). With HXB2, c-SRC but not PTK2B siRNA knockdown produced similar results.

CONCLUSIONS

Our results suggest c-SRC tyrosine kinase is a major regulator of HIV-1 infection, participating in multiple stages of infection post-entry: Reduced proviral integration with increased 2-LTR circles is reminiscent of integrase inhibitors used in combination antiretroviral therapy. Decreasing c-SRC expression and/or activity provides a new target for antiviral intervention and the potential for repurposing existing FDA-approved kinase inhibitors.

Interleukin 2-inducible T cell kinase (ITK) facilitates efficient egress of HIV-1 by coordinating Gag distribution and actin organization

Interleukin 2-inducible T cell kinase (ITK) influences T cell signaling by coordinating actin polymerization and polarization as well as recruitment of kinases and adapter proteins. ITK regulates multiple steps of HIV-1 replication, including virion assembly and release. Fluorescent microscopy was used to examine the functional interactions between ITK and HIV-1 Gag during viral particle release. ITK and Gag colocalized at the plasma membrane and were concentrated at sites of F-actin accumulation and membrane lipid rafts in HIV-1 infected T cells. There was polarized staining of ITK, Gag, and actin towards sites of T cell conjugates. Small molecule inhibitors of ITK disrupted F-actin capping, perturbed Gag-ITK colocalization, inhibited virus like particle release, and reduced HIV replication in primary human CD4+ T cells. These data provide insight as to how ITK influences HIV-1 replication and suggest that targeting host factors that regulate HIV-1 egress provides an innovative strategy for controlling HIV infection.

The human immunodeficiency virus coat protein gp120 promotes forward trafficking and surface clustering of NMDA receptors in membrane microdomains

Infection by the human immunodeficiency virus (HIV) can result in debilitating neurological syndromes collectively known as HIV-associated neurocognitive disorders. Although the HIV coat protein gp120 has been identified as a potent neurotoxin that enhances NMDA receptor function, the exact mechanisms for this effect are not known. Here we provide evidence that gp120 activates two separate signaling pathways that converge to enhance NMDA-evoked calcium flux by clustering NMDA receptors in modified membrane microdomains. gp120 enlarged and stabilized the structure of lipid microdomains on dendrites by mechanisms that involved a redox-regulated translocation of a sphingomyelin hydrolase (neutral sphingomyelinase-2) to the plasma membrane. A concurrent pathway was activated that accelerated the forward traffic of NMDA receptors by a PKA-dependent phosphorylation of the NR1 C-terminal serine 897 (masks an ER retention signal), followed by a PKC-dependent phosphorylation of serine 896 (important for surface expression). NMDA receptors were preferentially targeted to synapses and clustered in modified membrane microdomains. In these conditions, NMDA receptors were unable to laterally disperse and did not internalize, even in response to strong agonist induction. Focal NMDA-evoked calcium bursts were enhanced by threefold in these regions. Inhibiting membrane modification or NR1 phosphorylation prevented gp120 from accelerating the surface localization of NMDA receptors. Disrupting the structure of membrane microdomains after gp120 treatments restored the ability of NMDA receptors to disperse and internalize. These findings demonstrate that gp120 contributes to synaptic dysfunction in the setting of HIV infection by interfering with NMDA receptor trafficking.

Role of G protein-coupled vasoactive intestinal peptide receptors in HIV integration

The pathogenesis of HIV infection is closely linked to the replication of the virus in vivo. Even though the progress in anti-HIV-1 chemotherapy in the past several years has been dramatic, the efficient protection against HIV-1 infection still remains one of the most important global challenges. The complete blockage of AIDS progression appears to be difficult with current treatment due to the rapid occurrence of viral drug-resistance, increasing cost and the likelihood of adverse side effects. Furthermore, although originally regarded with high hope, development of a suitable vaccine appears to be years away. The purpose of this article is to describe previous findings regarding a potentially important role of the vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide (VPAC) family of G protein-coupled receptors in HIV-1 infection, to provide evidence for the involvement of these receptors in providing signals that can control the integration of the virus into the host DNA and to report new findings that support a role for VPAC receptors in the facilitation of HIV integration.

Patterns of HIV-1 protein interaction identify perturbed host-cellular subsystems

Human immunodeficiency virus type 1 (HIV-1) exploits a diverse array of host cell functions in order to replicate. This is mediated through a network of virus-host interactions. A variety of recent studies have catalogued this information. In particular the HIV-1, Human Protein Interaction Database (HHPID) has provided a unique depth of protein interaction detail. However, as a map of HIV-1 infection, the HHPID is problematic, as it contains curation error and redundancy; in addition, it is based on a heterogeneous set of experimental methods. Based on identifying shared patterns of HIV-host interaction, we have developed a novel methodology to delimit the core set of host-cellular functions and their associated perturbation from the HHPID. Initially, using biclustering, we identify 279 significant sets of host proteins that undergo the same types of interaction. The functional cohesiveness of these protein sets was validated using a human protein-protein interaction network, gene ontology annotation and sequence similarity. Next, using a distance measure, we group host protein sets and identify 37 distinct higher-level subsystems. We further demonstrate the biological significance of these subsystems by cross-referencing with global siRNA screens that have been used to detect host factors necessary for HIV-1 replication, and investigate the seemingly small intersect between these data sets. Our results highlight significant host-cell subsystems that are perturbed during the course of HIV-1 infection. Moreover, we characterise the patterns of interaction that contribute to these perturbations. Thus, our work disentangles the complex set of HIV-1-host protein interactions in the HHPID, reconciles these with siRNA screens and provides an accessible and interpretable map of infection.

The Src kinase Lck facilitates assembly of HIV-1 at the plasma membrane

HIV type 1 (HIV-1) assembly and egress are driven by the viral protein Gag and occur at the plasma membrane in T cells. Recent evidence indicates that secretory vesicles and machinery are essential components of virus packaging in both T cells and macrophages. However, the pathways and cellular mediators of Gag targeting to the plasma membrane are not well characterized. Lck, a lymphoid specific Src kinase critical for T cell activation, is found in the plasma membrane as well as various intracellular compartments and it has been suggested to influence HIV-1 replication. To investigate Lck as a potential regulator of Gag targeting, we assessed HIV-1 replication and Gag-induced virus-like particle release in the presence and absence of Lck. Release of HIV-1 and virus-like particles was reduced in the absence of Lck. This decrease in replication was not due to altered HIV-1 infection, transcription or protein translation. However, in T cells lacking Lck, HIV-1 accumulated intracellularly. In addition, expressing Lck in HeLa cells promoted HIV-1 Gag plasma membrane localization. Palmitoylation of the Lck unique domain, which is essential for directing Lck to the plasma membrane, was critical for its effect on HIV-1 replication. Furthermore, HIV-1 Gag directly interacted with the Lck unique domain in the context of infected cells. These results indicate that Lck plays a key role in targeting HIV-1 Gag to the plasma membrane in T cells.

High frequency of defective vpu compared with tat and rev genes in brain from patients with HIV type 1-associated dementia

Human immunodeficiency virus type 1 (HIV) infection of the central nervous system frequently causes HIV-associated dementia (HAD) and other neurological disorders. The role of HIV regulatory and accessory proteins in the pathogenesis of these disorders is unclear. Here we analyzed sequences of tat, rev, and vpu genes in 55 subgenomic clones previously shown to encode functional env genes from brain and lymphoid tissues of four AIDS patients with HAD. Phylogenetic analysis showed distinct compartmentalization of tat, rev, and vpu genes in brain versus lymphoid tissues. Nine of 19 vpu sequences from brain of two patients had premature stop codons at positions between amino acids 2 and 30, compared with 0 of 8 from lymphoid tissues. Tat sequences from brain (n = 8 of 8) but not lymphoid (n = 0 of 6) tissue from one patient had a 35 amino acid truncation at the C-terminus. Rev sequences from the brain of one patient (n = 6 of 8) had a 5 amino acid truncation. These results demonstrate a high frequency of defective vpu compared with tat and rev genes in brain from HAD patients, and identify sequence variants of these regulatory/accessory genes that may influence the pathogenesis of HIV-associated neurological disease.

The Sulfogalactose Moiety of Sulfoglycosphingolipids Serves as a Mimic of Tyrosine Phosphate in Many Recognition Processes

Multiple ligand co-recognition of 3'-sulfogalactosylceramide (SGC) and sulfotyrosine initiated the comparison of SGC and sulfotyrosine and, subsequently, phosphotyrosine (pY) binding. SGC is a receptor for ligands involved in cell adhesion/microbial pathology. pY forms a Src homology domain 2 recognition motif in intracellular signaling. Using hsp70, anti-SGC, and anti-pY antibodies, ligand binding is retained following phosphate/sulfate and tyrosine/galactose substitution in SGC and sulfate/phosphate exchange in pY. Remarkable lipid-dependent binding to phosphatidylethanolamine-conjugated sulfotyrosine suggests "microenvironmental" modulation of sulfotyrosine-containing receptors, similar to glycosphingolipids. Based on an aryl substrate-bound co-crystal of arylsulfatase A, a sulfogalactose and phosphotyrosine esterase, modeling provides a solvation basis for co-recognition. c-Src/Src homology domain 2:SGC/phosphogalactosylceramide binding confirms our hypothesis, heralding a carbohydrate-based approach to regulation of phosphotyrosine-mediated recognition.

HIV-1 infection is facilitated in T cells by decreasing p56lck protein tyrosine kinase activity

Several studies have suggested an important role for the protein tyrosine kinase p56lck (Lck) in HIV infection; however, the exact nature of this role remains unclear. Using a series of well characterized Jurkat-derived cell lines having a wide range of Lck kinase activity, our results showed that, while the entry of HIV-1 into these cell lines was similar, the kinetics of virus production by these cells were very different. Cells expressing a kinase-inactive Lck showed accelerated viral replication, whereas, cells expressing Lck with normal or elevated enzymatic activity showed a delay in virus replication that was proportional to the initial level of endogenous Lck activity. The cell line having the highest initial Lck kinase activity showed the slowest rate of productive HIV-1 infection. Analysis of 2-LTR circles revealed that this inhibitory effect of Lck was not due to inhibition of reverse transcription of HIV-1 genome or migration of the proviral DNA into the nuclei. This affect of Lck was confirmed in additional studies that used either the S1T cell line lacking completely Lck or where the Lck activity was altered in Jurkat cells prior to infection. S1T cells showed a 3- to 12-fold increase in the level of infection compared to Jurkat cells despite similar CD4 and chemokine coreceptor expression and cell doubling times. Pretreatment of Jurkat with an antisense lck oligodeoxynucleotide inhibited the synthesis of functional Lck and facilitated the viral replication by the cells as did expressing a dominant-negative mutant Lck which increased the productive infection>3-fold. Conversely, whereas IL-16 had no affect on productive infection in S1T cells that lack Lck, IL-16 pretreatment of Jurkat cells resulted in an immediate (within 5 min) and sustained and gradual (over 5 h) increase in Lck activity that resulted in a reduction of HIV-1 replication that paralleled the increasing Lck kinase activity. These results show that the enzymatic activity of Lck kinase can affect viral replication, that a lack of, or decreased Lck activity facilitates viral replication. Conversely, Lck can mediate a delay in HIV-1 infection that is proportional to the initial endogenous Lck enzyme activity.

VPAC1 is a cellular neuroendocrine receptor expressed on T cells that actively facilitates productive HIV-1 infection

OBJECTIVE

A lack of productive HIV-1 infection of Kit225 compared to Jurkat T cells, despite similar levels of CD4 and HIV-1 chemokine co-receptors, was found to correlate with the expression of vasoactive intestinal peptide/pituitary adenylate cyclase activating polypeptide receptor-1 (VPAC1). We therefore examined a role for this seven-transmembrane G protein-coupled neuroendocrine receptor in modulating HIV-1 infection.

METHODS

Reverse transcription-PCR was used to show the level of VPAC1 expression in different T-cell lines. A signal-blocking antibody to VPAC1 was used to examine its inhibiting effect on HIV-1 infection. Transfection of VPAC1 cDNA in both sense and anti-sense orientation was used to assess the role of VPAC1 in HIV-1 infection. HIV-1 infection was monitored by gag p24 ELISA using HIV-1IIIB or by luciferase activity using pseudo envelope-typed HXB2-NL4-3-luciferase. Analysis of HIV-1 gag DNA and 2-LTR circles was utilized to examine a possible mechanism for the effect of VPAC1.

RESULTS

Using VPAC1 signal blocking antibody, we showed that up to 80% of productive infection with HIV-1IIIB was inhibited. We also demonstrated that HIV-1 gp120 has sequence similarity to the natural ligand for VPAC1 and postulate that it can activate this receptor directly. Transfection of VPAC1 cDNA in the anti-sense orientation resulted in a significant loss, up to 50% of productive infection. In contrast, transfection of cells with VPAC1 in the sense orientation increased the productive infection by more than 15-fold and caused a profound increase in syncytium formation. Furthermore, stimulation of VPAC1 on primary cells facilitated in vitro infection with HIV-1 HXB2-NL4-3. Analysis of HIV-1 gag DNA indicated that VPAC1 does not affect viral entry; however, cells that show negligible expression of VPAC1 may not be productively infected as indicated by a lack of 2-LTR circle formation.

CONCLUSION

We have discovered a cellular receptor, VPAC1, that is a novel and potent facilitator of HIV-1 infection and thus, is a potentially important new target for therapeutic intervention.

Survey of reverse transcriptase from the heterosexual epidemic of human immunodeficiency virus type 1 CRF01_AE in Thailand from 1990 to 2000

Genetic diversity of the HIV-1 envelope gene has shown a steady increase over time in the Thai and other regional epidemics. A serial survey of subtype CRF01_AE polymerase gene (RT) diversity in Thailand was performed, using 48 novel and 15 reported sequences covering the period 1990--2000. These sequences were gathered from individuals whose sole risk factor for infection was heterosexual contact. By contrast to envelope, diversity was low and, despite a 40% increase early in the epidemic, has remained static since 1996. These results indicate that epidemic HIV-1 may be constrained within defined limits of genetic diversity at least in some genomic regions.

T-cell progenitor function during progressive human immunodeficiency virus-1 infection and after antiretroviral therapy

Impairment of T-cell renewal has been proposed as contributing to CD4+ T-cell depletion in persons infected with human immunodeficiency virus-1. We analyzed the T-cell development capacity of progenitors using fetal thymus organ culture. Those who progressed to AIDS had a dramatic loss in T-cell development capacity shortly after seroconversion. In contrast, long-term nonprogressors retained progenitor capacity 8 years after seroconversion. Approximately 70% of patients experienced an improvement in T-cell development capacity after receiving 6 months of potent antiretroviral therapy. Improvement in T-cell development in fetal thymus organ culture correlated with an increase in the number of naive CD4+ T cells in peripheral blood. Numbers of progenitors in blood and bone marrow after seroconversion or during therapy did not correlate with the change observed in T-cell development capacity. These data provide evidence that HIV-1 infection can interfere with T-cell renewal at the level of the progenitor cell. Interference with T-cell renewal may contribute to CD4+ T-cell depletion.

T-cell progenitor function during progressive human immunodeficiency virus-1 infection and after antiretroviral therapy

Impairment of T-cell renewal has been proposed as contributing to CD4+ T-cell depletion in persons infected with human immunodeficiency virus-1. We analyzed the T-cell development capacity of progenitors using fetal thymus organ culture. Those who progressed to AIDS had a dramatic loss in T-cell development capacity shortly after seroconversion. In contrast, long-term nonprogressors retained progenitor capacity 8 years after seroconversion. Approximately 70% of patients experienced an improvement in T-cell development capacity after receiving 6 months of potent antiretroviral therapy. Improvement in T-cell development in fetal thymus organ culture correlated with an increase in the number of naive CD4+ T cells in peripheral blood. Numbers of progenitors in blood and bone marrow after seroconversion or during therapy did not correlate with the change observed in T-cell development capacity. These data provide evidence that HIV-1 infection can interfere with T-cell renewal at the level of the progenitor cell. Interference with T-cell renewal may contribute to CD4+ T-cell depletion.

Altered replication of human immunodeficiency virus type 1 (HIV-1) in T cell lines retrovirally transduced to express Herpesvirus saimiri proteins StpC and/or Tip

Human peripheral blood T lymphocytes are transformed in vitro to continuous proliferation by Herpesvirus saimiri subgroup C strains. It has been previously shown that H. saimiri-transformed human T cell lines are a permissive system for HIV-1 and 2 replication and are highly susceptible to infection by HIV-1 and 2. Two open reading frames of H. saimiri, StpC and Tip, are required for T cell transformation and are unique to this herpesvirus. The successful transduction of human T cells with retroviral vectors expressing H. saimiri proteins StpC and Tip has allowed us to extend the previously mentioned observations and investigate the role of StpC and Tip in replication of HIV-1 T-tropic strains (IIIB, MN, and RF) in human T cell lines. StpC expression in Molt4 dramatically enhanced HIV-1 replication as measured by Tat protein expression, syncytia formation, and accumulation of reverse transcriptase activity. In contrast, Tip expression in Molt4 cells inhibited HIV-1 replication and cytopathic effects relative to Molt4 cells transduced with the empty vector alone. The StpC-induced phenotype dominated in Molt4 cells transduced to express both StpC and Tip, suggesting that StpC is responsible for facilitating HIV-1 replication in H. saimiri-transformed T cells. Colony-forming ability of Tip-expressing Molt4 cells following HIV-1 infection was greatly enhanced over Molt4 cells expressing either StpC or no H. saimiri proteins at all. HIV-1 proviral DNA could be detected by PCR in surviving Molt4 cells expressing StpC or Tip, indicating that a persistent infection was established. A better understanding of the effects of Tip and StpC proteins on the biology of human hemopoietic stem cells may lead to novel therapeutic interventions for the treatment of AIDS.

Human immunodeficiency virus type 1 induction mediated by genistein is linked to cell cycle arrest in G2

Protein tyrosine kinase (PTK) phosphorylation is involved in cellular proliferation and differentiation processes that are key factors for human immunodeficiency virus type 1 (HIV-1) regulation in infected monocytic cells. Short-term exposure of the chronically infected promyelocytic OM10 cell line with the PTK inhibitor genistein induced a dose-dependent increase in p24 antigen production in culture supernatants. This induction persisted in the presence of the reverse transcriptase inhibitor, zidovudine, and was associated with an increased transcription of HIV-1 multiply spliced and unspliced RNAs, suggesting a transcriptional mechanism targeting the integrated provirus. Genistein induced cell differentiation, apoptosis, and a G2 arrest in the OM10 cells. Cell differentiation and apoptosis were not directly involved in the observed increase in HIV-1 replication that was closely linked to genistein-induced G2 arrest. Alleviation of the G2 arrest by pentoxyfylline resulted in a concomitant reduction of HIV-1 to baseline replication. Additionally, by flow cytometry, a significant increase in the number of p24 antigen-expressing cells was observed in cells arrested in G2 compared to those located in G1 or S. Tyrosine kinase inhibition was found not to be essential for enhanced viral replication, which seemed to be related to two other properties of genistein, inhibition of topoisomerase II activity and inhibition of phosphotidylinositol turnover. These findings are consistent with the recent observation that HIV-1 Vpr induces viral replication through preventing proliferation of cells by arresting them in G2 of the cell cycle and strongly suggest that manipulation of the cell cycle plays an important role in HIV-1 pathogenesis.

The protein tyrosine kinase p56lck is required for triggering NF-kappaB activation upon interaction of human immunodeficiency virus type 1 envelope glycoprotein gp120 with cell surface CD4

We have previously shown that NF-kappaB nuclear translocation can be observed upon human immunodeficiency virus type 1 (HIV-1) binding to cells expressing the wild-type CD4 molecule, but not in cells expressing a truncated form of CD4 that lacks the cytoplasmic domain (M. Benkirane, K.-T. Jeang, and C. Devaux, EMBO J. 13:5559-5569, 1994). This result indicated that the signaling cascade which controls HIV-1-induced NF-kappaB activation requires the integrity of the CD4 cytoplasmic tail and suggested the involvement of a second protein that binds to this portion of the molecule. Here we investigate the putative role of p56(lck) as a possible cellular intermediate in this signal transduction pathway. Using human cervical carcinoma HeLa cells stably expressing CD4, p56(lck), or both molecules, we provide direct evidence that expression of CD4 and p56(lck) is required for HIV-1-induced NF-kappaB translocation. Moreover, the fact that HIV-1 stimulation did not induce nuclear translocation of NF-kappaB in cells expressing a mutant form of CD4 at position 420 (C420A) and the wild-type p56(lck) indicates the requirement for a functional CD4-p56(lck) complex.

Inhibition of human immunodeficiency virus type 1 virion entry by dominant-negative Hck

To study the role of Src family tyrosine kinases in infection with human immunodeficiency virus type 1 (HIV-1), we constructed an Hck mutant, HckN, that hinders signaling from wild-type Hck. HIV-1 produced in HckN-expressing cells was significantly less infectious to HeLa-CD4-LTR-beta-gal (MAGI) cells than HIV-1 produced in mock-transfected cells. The inhibitory effect of HckN was compensated for by the expression of vesicular stomatitis virus G protein. Finally, we found that the HIV-1 produced in the HckN-expressing cells entered into the cells less efficiently than did the control HIV-1. These results suggest that the Src family tyrosine kinases regulate entry of HIV-1 into target cells.

Cutting Edge: HIV-1 Infection Induces a Selective Reduction in STAT5 Protein Expression

HIV-1 infection is accompanied by qualitative and quantitative defects in CD4+ T lymphocytes. Loss of immune function in HIV patients is usually associated with a profound dysregulation of cytokine production. To investigate whether cytokine signaling defects occur during HIV infection, PHA blasts from healthy human donors were infected with two strains of HIV-1 and screened for the expression of STAT proteins used in cytokine signaling. A selective decrease in STAT5B was seen 8 days after infection with the BZ167 dual-tropic HIV isolate, but not with the Ba-L, M-tropic strain. Based on these findings, purified T cells from HIV-infected patients in different stages of disease were also tested for STAT expression; decreases in STAT5A, STAT5B, and STAT1α were observed in all patients. The reduction in STATs seen in vivo and in vitro after HIV infection may contribute to the loss of T cell function in HIV disease.

Increased Enzymatic Activity of the T-Cell Antigen Receptor-Associated Fyn Protein Tyrosine Kinase in Asymptomatic Patients Infected With the Human Immunodeficiency Virus

The immune system of patients infected with human immunodeficiency virus (HIV) is in a state of chronic activation; however, the nature of HIV-related immune activation is unknown. As normal T-cell activation involves early tyrosine phosphorylation induced by the T-cell antigen receptor-associated src-family protein tyrosine kinase p59fyn(T) (Fyn), we examined a potential role for this kinase in HIV-related immune dysfunction. We determined the relative specific kinase activity of Fyn in lysates of peripheral blood mononuclear cells from 47 normal control individuals tested negative for HIV-1 and -2, human T-cell lymphotropic virus Type I, hepatitis B virus (HBV), hepatitis C virus (HCV), and syphilis; 14 asymptomatic HIV-infected patients having near-normal CD4+ T-cell counts (350 to 980 CD4+ cells/μL); 4 patients with symptomatic acquired immunodeficiency syndrome (AIDS) (<30 CD4+ cells/μL); 13 patients having chronic infection with HBV (6 patients) or HCV (7 patients); and 6 patients with systemic lupus erythematosis (SLE). All patients with asymptomatic HIV disease were shown to have a profound increase (mean increase of 19-fold; range threefold to 56-fold increase; p = 1.33 × 10−9) in the relative specific kinase activity of Fyn compared to uninfected controls or patients with hepatitis or SLE. In contrast, patients with AIDS had an Fyn-specific kinase activity that was much less affected (mean increase of threefold; range onefold to sevenfold increase; p = 1.30 × 10−5). It was further shown that HIV infection affects the Fyn-specific kinase activity in CD8+-enriched cells, suggesting abnormal Fyn activity in both CD8+ as well as CD4+ T lymphocytes. Initial results implicate a role for the CSK protein tyrosine kinase as responsible for the abnormal Fyn kinase activity observed in HIV-infected patients. These data indicate early and chronic activation of Fyn as a unique HIV-related effect that has the potential to be diagnostic for early HIV infection and/or may serve as a prognostic indicator for advancement to full-blown AIDS. More importantly, sustained activation of the protein tyrosine kinase associated with T-cell antigen receptor function may result in, or contribute to, the immunopathogenic effects associated with HIV infection.