Tat protein induces self-perpetuating permissivity for productive HIV-1 infection

We report that human immunodeficiency virus type 1 (HIV-1) has evolved a self-perpetuating mechanism to actively generate cells permissive for productive and cytopathic infection. Only activated T cells can be productively infected, which leads to their rapid depletion (2 × 10⁹/day in an infected individual). Establishment of productive HIV-1 infection therefore requires continual activations from the large pool of quiescent T cells. Tat protein, which is secreted by infected cells, activated uninfected quiescent T cells in vitro and in vivo. These Tat-activated uninfected cells became highly permissive for productive HIV-1 infection. Activation of primary T cells by Tat protein involved integrin receptors and was associated with activation of mitogen-activated protein kinases, including ERK1 and JNK kinase. Accordingly, these primary T cells progressed from G₀ to the late G₁ phase of the cell cycle.     

HIV-1 Tat protein mimicry of chemokines

The HIV-1 Tat protein is a potent chemoattractant for monocytes. We observed that Tat shows conserved amino acids corresponding to critical sequences of the chemokines, a family of molecules known for their potent ability to attract monocytes. Synthetic Tat and a peptide (CysL_24–51) encompassing the “chemokine-like” region of Tat induced a rapid and transient Ca²⁺ influx in monocytes and macrophages, analogous to β-chemokines. Both monocyte migration and Ca²⁺ mobilization were pertussis toxin sensitive and cholera toxin insensitive. Cross-desensitization studies indicated that Tat shares receptors with MCP-1, MCP-3, and eotaxin. Tat was able to displace binding of β-chemokines from the β-chemokine receptors CCR2 and CCR3, but not CCR1, CCR4, and CCR5. Direct receptor binding experiments with the CysL_24–51 peptide confirmed binding to cells transfected with CCR2 and CCR3. HIV-1 Tat appears to mimic β-chemokine features, which may serve to locally recruit chemokine receptor-expressing monocytes/macrophages toward HIV producing cells and facilitate activation and infection.     

Anti-HIV-1 and chemotactic activities of human stromal cell-derived factor 1α (SDF-1α) and SDF-1β are abolished by CD26/dipeptidyl peptidase IV-mediated cleavage

CD26 is a leukocyte-activation antigen that is expressed on T lymphocytes and macrophages and possesses dipeptidyl peptidase IV (DPPIV) activity, whose natural substrates have not been identified yet. CXC chemokines, stromal cell-derived factor 1α (SDF-1α) and 1β (SDF-1β), sharing the receptor CXCR-4, are highly efficacious chemoattractants for resting lymphocytes and CD34⁺ progenitor cells, and they efficiently block the CXCR-4-mediated entry into cells of T cell line tropic strains of HIV type 1 (HIV-1). Here we show that both the chemotactic and antiviral activities of these chemokines are abrogated by DPPIV-mediated specific removal of the N-terminal dipeptide, not only when the chemokines are produced in transformed mouse L cell line to express human CD26 but also when they were exposed to a human T cell line (H9) physiologically expressing CD26. Mutagenesis of SDF-1α confirmed the critical requirement of the N-terminal dipeptide for its chemotactic and antiviral activities. These data suggest that CD26-mediated cleavage of SDF-1α and SDF-1β likely occurs in human bodies and promotes HIV-1 replication and disease progression. They may also explain why memory function of CD4⁺ cells is preferentially lost in HIV-1 infection. Furthermore, CD26 would modulate various other biological processes in which SDF-1α and SDF-1β are involved.     

Decrease in peripheral type 1 over type 2 T cell cytokine production in patients with rheumatoid arthritis correlates with an increase in severity of disease

Objectives—To compare peripheral type 1 (T1) and type 2 (T2) T cell activities in rheumatoid arthritis (RA) patients with that found for osteoarthritic (OA) patients and healthy controls and to correlate peripheral T1/T2 cell activity in RA with parameters of the disease.
METHODS—Peripheral blood mononuclear cells were isolated from patients with RA (n=66), OA (n=19), and healthy controls (n=15). Primary T cell activity in these mononuclear cells was enhanced by means of anti-CD3/anti-CD28, which mimicks stimulation of T cells by activation of the T cell receptor and a major co-stimulatory signal. Interferon gamma (IFNγ) production and interleukin 4 (IL4) production in the three groups were quantified as measures of T1 and T2 cell activity, respectively, and compared. Serum tumour necrosis factor α (TNFα), erythrocyte sedimentation rate (ESR), C reactive protein (CRP), and joint destruction assessed radiographically of RA patients were determined as parameters of disease activity and correlated with T1/T2 cell activity.
RESULTS—Peripheral T cells from RA patients produced significantly less IFNγ and more IL4 than T cells from both age and sex matched OA patients and healthy controls. Moreover, in RA patients both a decrease in IFNγ and an increase in IL4 production correlated with an increase in serum TNFα, ESR, CRP, and joint destruction.
Conclusions—These results suggest a role for differential T cell activity in RA. In view of the intra-articular T1 cell predominance the results might be explained by selective T1 cell migration into the joint or peripheral suppression of T1 cell activity.

     

Interferon α2–Thymosin α1 Fusion Protein (IFNα2–Tα1): A Genetically Engineered Fusion Protein with Enhanced Anticancer and Antiviral Effect

Human interferon α2 (IFNα2) and thymosin α1 (Tα1) are therapeutic proteins used for the treatment of viral infections and different types of cancer. Both IFNα2 and Tα1 show a synergic effect in their activities when used in combination. Furthermore, the therapeutic fusion proteins produced through the genetic fusion of two genes can exhibit several therapeutic functions in one molecule. In this study, we determined the anticancer and antiviral effect of human interferon α2–thymosin α1 fusion protein (IFNα2–Tα1) produced in our laboratory for the first time. The cytotoxic and genotoxic effect of IFNα2–Tα1 was evaluated in HepG2 and MDA-MB-231 cells. The in vitro assays confirmed that IFNα2–Tα1 inhibited the growth of cells more effectively than IFNα2 alone and showed an elevated genotoxic effect. The expression of proapoptotic genes was also significantly enhanced in IFNα2–Tα1-treated cells compared to IFNα2-treated cells. Furthermore, the HCV RNA level was significantly reduced in IFNα2–Tα1-treated HCV-infected Huh7 cells compared to IFNα2-treated cells. The quantitative PCR analysis showed that the expression of various genes, the products of which inhibit HCV replication, was significantly enhanced in IFNα2–Tα1-treated cells compared to IFNα2-treated cells. Our findings demonstrate that IFNα2–Tα1 is more effective than single IFNα2 as an anticancer and antiviral agent.     

The integrin α4β7 forms a complex with cell-surface CD4 and defines a T-cell subset that is highly susceptible to infection by HIV-1

Both activated and resting CD4⁺ T cells in mucosal tissues play important roles in the earliest phases of infection after sexual transmission of HIV-1, a process that is inefficient. HIV-1 gp120 binds to integrin α₄β₇ (α₄β₇), the gut mucosal homing receptor. We find that α₄β₇^high CD4⁺ T cells are more susceptible to productive infection than are α₄β₇^low-neg CD4⁺ T cells in part because this cellular subset is enriched with metabolically active CD4⁺ T cells. α₄β₇^high CD4⁺ T cells are CCR5^high and CXCR4^low; on these cells, α₄β₇ appears in a complex with CD4. The specific affinity of gp120 for α₄β₇ provides a mechanism for HIV-1 to target activated cells that are critical for efficient virus propagation and dissemination following sexual transmission.     

Fas expression by tumor stroma is required for cancer eradication

The contribution of molecules such as perforin, IFN-γ (IFNγ), and particularly Fas ligand (FasL) by transferred CD8⁺ effector T (T_E) cells to rejection of large, established tumors is incompletely understood. Efficient attack against large tumors carrying a surrogate tumor antigen (mimicking a “passenger” mutation) by T_E cells requires action of IFNγ on tumor stroma cells to avoid selection of antigen-loss variants. Because “cancer-driving” antigens (CDAs) are rarely counterselected, IFNγ may be expected to be dispensable in elimination of cancers by targeting a CDA. Here, initial regression of large, established tumors required neither IFNγ, FasL, nor perforin by transferred CD8⁺ T_E cells targeting Simian Virus (SV) 40 large T as CDA. However, cytotoxic T_E cells lacking IFNγ or FasL could not prevent relapse despite retention of the rejection antigen by the cancer cells. Complete tumor rejection required IFNγ-regulated Fas by the tumor stroma. Therefore, T_E cells lacking IFNγ or FasL cannot prevent progression of antigenic cancer because the tumor stroma escapes destruction if its Fas expression is down-regulated.     

Characterization of Adaptive-like γδ T Cells in Ugandan Infants during Primary Cytomegalovirus Infection

Gamma-delta (γδ) T cells are unconventional T cells that help control cytomegalovirus (CMV) infection in adults. γδ T cells develop early in gestation, and a fetal public γδ T cell receptor (TCR) clonotype is detected in congenital CMV infections. However, age-dependent γδ T cell responses to primary CMV infection are not well-understood. Flow cytometry and TCR sequencing was used to comprehensively characterize γδ T cell responses to CMV infection in a cohort of 32 infants followed prospectively from birth. Peripheral blood γδ T cell frequencies increased during infancy, and were higher among CMV-infected infants relative to uninfected. Clustering analyses revealed associations between CMV infection and activation marker expression on adaptive-like Vδ1 and Vδ3, but not innate-like Vγ9Vδ2 γδ T cell subsets. Frequencies of NKG2C⁺CD57⁺ γδ T cells were temporally associated with the quantity of CMV shed in saliva by infants with primary infection. The public γδ TCR clonotype was only detected in CMV-infected infants <120 days old and at lower frequencies than previously described in fetal infections. Our findings support the notion that CMV infection drives age-dependent expansions of specific γδ T cell populations, and provide insight for novel strategies to prevent CMV transmission and disease.     

Antibodies to several conformation-dependent epitopes of gp120/gp41 inhibit CCR-5-dependent cell-to-cell fusion mediated by the native envelope glycoprotein of a primary macrophage-tropic HIV-1 isolate

The β-chemokine receptor CCR-5 is essential for the efficient entry of primary macrophage-tropic HIV-1 isolates into CD4⁺ target cells. To study CCR-5-dependent cell-to-cell fusion, we have developed an assay system based on the infection of CD4⁺ CCR-5⁺ HeLa cells with a Semliki Forest virus recombinant expressing the gp120/gp41 envelope (Env) from a primary clade B HIV-1 isolate (BX08), or from a laboratory T cell line-adapted strain (LAI). In this system, gp120/gp41 of the “nonsyncytium-inducing,” primary, macrophage-tropic HIV-1_BX08 isolate, was at least as fusogenic as that of the “syncytium-inducing” HIV-1_LAI strain. BX08 Env-mediated fusion was inhibited by the β-chemokines RANTES (regulated upon activation, normal T cell expressed and secreted) and macrophage inflammatory proteins 1β (MIP-1β) and by antibodies to CD4, whereas LAI Env-mediated fusion was insensitive to these β-chemokines. In contrast soluble CD4 significantly reduced LAI, but not BX08 Env-mediated fusion, suggesting that the primary isolate Env glycoprotein has a reduced affinity for CD4. The domains in gp120/gp41 involved in the interaction with the CD4 and CCR-5 molecules were probed using monoclonal antibodies. For the antibodies tested here, the greatest inhibition of fusion was observed with those directed to conformation-dependent, rather than linear epitopes. Efficient inhibition of fusion was not restricted to epitopes in any one domain of gp120/gp41. The assay was sufficiently sensitive to distinguish between antibody- and β-chemokine-mediated fusion inhibition using serum samples from patient BX08, suggesting that the system may be useful for screening human sera for the presence of biologically significant antibodies.     

An interleukin 4 (IL-4)-independent pathway for CD4+ T cell IL-4 production is revealed in IL-4 receptor-deficient mice

IL-4 receptor α chain (IL-4Rα)-deficient mice were generated by gene-targeting in BALB/c embryonic stem cells. Mutant mice showed a loss of IL-4 signal transduction and functional activity. The lack of IL-4Rα resulted in markedly diminished, but not absent, TH2 responses after infection with the helminthic parasite Nippostrongylus brasiliensis. CD4⁺, CD62L-high, and CD62L-low T cell populations from uninfected IL-4Rα^−/− mice were isolated by cell sorting. Upon primary stimulation by T cell receptor cross-linkage, the CD62L-low, but not the CD62L-high, cells secreted considerable amounts of IL-4, which was strikingly enhanced upon 4-day culture with anti-CD3 in the presence or absence of IL-4. CD62L-low cells isolated from IL-4Rα^−/−, β₂-microglobulin^−/− double homozygous mice produced less IL-4 than did either IL-4Rα^−/− or wild-type mice. These results indicate that an IL-4-independent, β₂-microglobulin-dependent pathway exists through which the CD62L-low CD4⁺ population has acquired IL-4-producing capacity in vivo, strongly suggesting that these cells are NK T cells.     

Lysis of HIV-1-infected cells and inhibition of viral replication by universal receptor T cells

Increasing evidence suggests that HIV-1-specific cytotoxic T lymphocytes (CTLs) are a key host immune response to HIV-1 infection. Generation of CTL responses for prevention or therapy of HIV-1 infection has several intrinsic technical barriers such as antigen expression and presentation, the varying HLA restrictions between different individuals, and the potential for viral escape by sequence variation or surface molecule alteration on infected cells. A strategy to circumvent these limitations is the construction of a chimeric T cell receptor containing human CD4 or HIV-1-specific Ig sequences linked to the signaling domain of the T cell receptor ζ chain (universal T cell receptor). CD8⁺ CTLs transduced with this universal receptor can then bind and lyse infected cells that express surface HIV-1 gp120. We evaluated the ability of universal-receptor-bearing CD8⁺ cells from a seronegative donor to lyse acutely infected cells and inhibit HIV-1 replication in vitro. The kinetics of lysis and efficiency of inhibition were comparable to that of naturally occurring HIV-1-specific CTL clones isolated from infected individuals. Further study will be required to determine the utility of these cells as a therapeutic strategy in vivo.     

Visualization of IFNβ production by plasmacytoid versus conventional dendritic cells under specific stimulation conditions in vivo

Type I interferons, a protein family of multiple IFNαs and a single IFNβ, initially identified on the basis of their antiviral activities have recently been attributed important roles in bacterial and parasitic infections. To assess the cellular sources of IFNβ, the IFN produced first in most situations, we created an IFNβ reporter-knockin mouse, in which yellow fluorescent protein (YFP) is expressed from a bicistronic mRNA linked by an internal ribosomal entry site to the endogenous IFNβ mRNA. This YFP expression allows spatiotemporal tracking of the initiation of the type I IFN response on a single-cell level. In vitro bone marrow-derived macrophages (BMMΦs) and bone marrow-derived dendritic cells (BMDCs) show IFNβ production from distinct cell subpopulations in response to defined pathogen compounds. A subpopulation of GMCSF-derived BMDCs produced IFNβ after poly(I:C), 3′5′-cytidylylguanosine (CpG), or LPS treatment, whereas Flt3-L-cultured plasmacytoid DCs (pDCs) responded mainly to CpG. After poly(I:C) injection in vivo, IFNβ-producing cells localize to the splenic marginal zone and the lymph node subcapsular sinus. Infection with murine cytomegalovirus (MCMV) induces IFNβ/YFP expression exclusively in few activated pDCs at the T cell/B cell interface of the splenic white pulp. This IFNβ/YFP reporter mouse represents a reliable tool for the visualization and characterization of IFNβ-producing cells in vitro and in vivo.     

Development and function of T cells in T cell antigen receptor/CD3 ζ knockout mice reconstituted with FcɛRI γ

Engagement of α–β T cell receptors (TCRs) induces many events in the T cells bearing them. The proteins that transduce these signals to the inside of cells are the TCR-associated CD3 polypeptides and ζ–ζ or ζ–η dimers. Previous experiments using knockout (KO) mice that lacked ζ (ζKO) showed that ζ is required for good surface expression of TCRs on almost all T cells and for normal T cell development. Surprisingly, however, in ζKO mice, a subset of T cells in the gut of both ζKO and normal mice bore nearly normal levels of TCR on its surface. This was because ζ was replaced by the FcRI γ (FcRγ). These cells were relatively nonreactive to stimuli via their TCRs. In addition, a previous report showed that ζ replacement by the FcRγ chain also might occur on T cells in mice bearing tumors long term. Again, these T cells were nonreactive. To understand the consequences of ζ substitution by FcRγ for T cell development and function in vivo, we produced ζKO mice expressing FcRγ in all of their T cells (FcRγTG ζKO mice). In these mice, TCR expression on immature thymocytes was only slightly reduced compared with controls, and thymocyte selection occurred normally and gave rise to functional, mature T cells. Therefore, the nonreactivity of the FcRγ⁺ lymphocytes in the gut or in tumor-bearing mice must be caused by some other phenomenon. Unexpectedly, the TCR levels of mature T cells in FcRγTG ζKO mice were lower than those of controls. This was particularly true for the CD4⁺ T cells. We conclude that FcRγ can replace the functions of ζ in T cell development in vivo but that TCR/CD3 complexes associated with FcRγ rather than ζ are less well expressed on cells. Also, these results revealed a difference in the regulation of expression of the TCR/CD3 complex on CD4⁺ and CD8⁺ T cells.     

CD8+ T-cell-derived soluble factor(s), but not β-chemokines RANTES, MIP-1α, and MIP-1β, suppress HIV-1 replication in monocyte/macrophages

It has been demonstrated that CD8⁺ T cells produce a soluble factor(s) that suppresses human immunodeficiency virus (HIV) replication in CD4⁺ T cells. The role of soluble factors in the suppression of HIV replication in monocyte/macrophages (M/M) has not been fully delineated. To investigate whether a CD8⁺ T-cell-derived soluble factor(s) can also suppress HIV infection in the M/M system, primary macrophages were infected with the macrophage tropic HIV-1 strain Ba-L. CD8⁺ T-cell-depleted peripheral blood mononuclear cells were also infected with HIV-1 IIIB or Ba-L. HIV expression from the chronically infected macrophage cell line U1 was also determined in the presence of CD8⁺ T-cell supernatants or β-chemokines. We demonstrate that: (i) CD8⁺ T-cell supernatants did, but β-chemokines did not, suppress HIV replication in the M/M system; (ii) antibodies to regulated on activation normal T-cell expressed and Secreted (RANTES), macrophage inflammatory protein 1α (MIP-1α) and MIP-1β did not, whereas antibodies to interleukin 10, interleukin 13, interferon α, or interferon γ modestly reduced anti-HIV activity of the CD8⁺ T-cell supernatants; and (iii) the CD8⁺ T-cell supernatants did, but β-chemokines did not, suppress HIV-1 IIIB replication in peripheral blood mononuclear cells as well as HIV expression in U1 cells. These results suggest that HIV-suppressor activity of CD8⁺ T cells is a multifactorial phenomenon, and that RANTES, MIP-1α, and MIP-1β do not account for the entire scope of CD8⁺ T-cell-derived HIV-suppressor factors.     

Hyaluronan production in human rheumatoid fibroblastic synovial lining cells is increased by interleukin 1β but inhibited by transforming growth factor β1

OBJECTIVES—To investigate the regulatory roles of interleukin 1β (IL1β), tumour necrosis factor α (TNFα), interferon γ (IFNγ) or transforming growth factor β1 (TGFβ1) on hyaluronan (HA) synthesis by human fibroblastic synovial lining cells.
METHODS—Concentrations of HA in culture supernatants of fibroblastic synovial lining cell line (RAMAK-1 cell line) with or without stimulation by IL1β, TNFα, IFNγ or TGFβ1 were measured by sandwich binding protein assay. Levels of HA synthase mRNA of the cells with or without stimulation were detected by reverse transcribed polymerase chain reaction. Molecular weights of HA in the culture supernatants of the cells with or without stimulation were measured using high performance gel permeation liquid chromatography.
RESULTS—HA synthesis by the cells was not significantly augmented by TNFα or by IFNγ. It was significantly stimulated by IL1β but inhibited by TGFβ1. Molecular weights of HA in the culture supernatants of the cells were unchanged by stimulation with TNFα. They were remarkably increased by stimulation with IL1β and IFNγ, but reduced with TGFβ1.
CONCLUSION—IL1β is an up regulator of HA synthesis, while TGFβ1 is a down regulator. HA production in the synovial lining cells of inflamed joints (for example, rheumatoid arthritis) might be regulated by the balance of these cytokines.

Keywords: synovial lining cells; hyaluronan, interleukin 1β; transforming growth factor β1     

TRIM5α Restriction of HIV-1-N74D Viruses in Lymphocytes Is Caused by a Loss of Cyclophilin A Protection

The core of HIV-1 viruses bearing the capsid change N74D (HIV-1-N74D) do not bind the human protein CPSF6. In primary human CD4⁺ T cells, HIV-1-N74D viruses exhibit an infectivity defect when compared to wild-type. We first investigated whether loss of CPSF6 binding accounts for the loss of infectivity. Depletion of CPSF6 in human CD4⁺ T cells did not affect the early stages of wild-type HIV-1 replication, suggesting that defective infectivity in the case of HIV-1-N74D viruses is not due to the loss of CPSF6 binding. Based on our previous result that cyclophilin A (Cyp A) protected HIV-1 from human tripartite motif-containing protein 5α (TRIM5α_hu) restriction in CD4⁺ T cells, we found that depletion of TRIM5α_hu in CD4⁺ T cells rescued the infectivity of HIV-1-N74D, suggesting that HIV-1-N74D cores interacted with TRIM5α_hu. Accordingly, TRIM5α_hu binding to HIV-1-N74D cores was increased compared with that of wild-type cores, and consistently, HIV-1-N74D cores lost their ability to bind Cyp A. In agreement with the notion that N74D capsids are defective in their ability to bind Cyp A, we found that HIV-1-N74D viruses were 20-fold less sensitive to TRIMCyp restriction when compared to wild-type viruses in OMK cells. Structural analysis revealed that N74D hexameric capsid protein in complex with PF74 is different from wild-type hexameric capsid protein in complex with PF74, which explains the defect of N74D capsids to interact with Cyp A. In conclusion, we showed that the decreased infectivity of HIV-1-N74D in CD4⁺ T cells is due to a loss of Cyp A protection from TRIM5α_hu restriction activity.     

Detection of IFNγ-Secreting CD4+ and CD8+ Memory T Cells in COVID-19 Convalescents after Stimulation of Peripheral Blood Mononuclear Cells with Live SARS-CoV-2

Background: New coronavirus SARS-CoV-2, a causative agent of the COVID-19 pandemic, has been circulating among humans since November 2019. Multiple studies have assessed the qualitative and quantitative characteristics of virus-specific immunity in COVID-19 convalescents, however, some aspects of the development of memory T-cell responses after natural SARS-CoV-2 infection remain uncovered. Methods: In most of published studies T-cell immunity to the new coronavirus is assessed using peptides corresponding to SARS-CoV-1 or SARS-CoV-2 T-cell epitopes, or with peptide pools covering various parts of the viral proteins. Here, we determined the level of CD4⁺ and CD8⁺ memory T-cell responses in COVID-19 convalescents by stimulating PBMCs collected 1 to 6 months after recovery with sucrose gradient-purified live SARS-CoV-2. IFNγ production by the central and effector memory helper and cytotoxic T cells was assessed by intracellular cytokine staining assay and flow cytometry. Results: Stimulation of PBMCs with live SARS-CoV-2 revealed IFNγ-producing T-helper effector memory cells with CD4⁺CD45RA⁻CCR7⁻ phenotype, which persisted in circulation for up to 6 month after COVID-19. In contrast, SARS-CoV-2-specific IFNγ-secreting cytotoxic effector memory T cells were found at significant levels only shortly after the disease, but rapidly decreased over time. Conclusion: The stimulation of immune cells with live SARS-CoV-2 revealed a rapid decline in the pool of effector memory CD8⁺, but not CD4⁺, T cells after recovery from COVID-19. These data provide additional information on the development and persistence of cellular immune responses after natural infection, and can inform further development of T cell-based SARS-CoV-2 vaccines.     

CD40 ligand (CD154) stimulation of macrophages to produce HIV-1-suppressive β-chemokines

β-chemokines play an important role in the development of immunologic reactions. Macrophages are major β-chemokine-producing cells during T-cell directed, delayed-type hypersensitivity reactions in tissues, and have been reported to be important producers of β-chemokines in the lymph nodes of HIV-1-infected individuals. However, the physiological signals responsible for inducing macrophages to produce β-chemokines have not been established. Two soluble T cell products, interferon-γ and granulocyte-macrophage colony stimulating factor, were added to cultured macrophages, but failed to stimulate the production of macrophage inflammatory protein-1α and -1β; regulated upon activation, normal T cell expressed and secreted (RANTES); or monocyte chemoattractant protein-1. Instead, direct cell–cell contact between macrophages and cells engineered to express CD40L (also known as CD154) resulted in the production of large amounts of macrophage inflammatory protein-1α and -1β, and RANTES (all ligands for CCR5), and monocyte chemoattractant protein-1 (a ligand for CCR2). Supernatants from CD40L-stimulated macrophages protected CD4⁺ T cells from infection by a nonsyncytium-inducing strain of HIV-1 (which uses CCR5 as a coreceptor). These results have implications for granulomatous diseases, and conditions such as atherosclerosis and multiple sclerosis, where CD40L-bearing cells have been found in the macrophage-rich lesions where β-chemokines are being produced. Overall, these findings define a pathway linking the specific recognition of antigen by T cells to the production of β-chemokines by macrophages. This pathway may play a role in anti-HIV-1 immunity and the development of immunologic reactions or lesions.