Differential regulation of VLA-2 expression on Th1 and Th2 cells: a novel marker for the classification of Th subsets

Integrins meet complement: The evolutionary tip of an iceberg orchestrating metabolism and immunity

Immunologists have recently realized that there is more to the classic innate immune sensor systems than just mere protection against invading pathogens. It is becoming increasingly clear that such sensors, including the inflammasomes, toll-like receptors, and the complement system, are heavily involved in the regulation of basic cell physiological processes and particularly those of metabolic nature. In fact, their "non-canonical" activities make sense as no system directing immune cell activity can perform such task without the need for energy. Further, many of these ancient immune sensors appeared early and concurrently during evolution, particularly during the developmental leap from the single-cell organisms to multicellularity, and therefore crosstalk heavily with each other. Here, we will review the current knowledge about the emerging cooperation between the major inter-cell communicators, integrins, and the cell-autonomous intracellularly and autocrine-active complement, the complosome, during the regulation of single-cell metabolism. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

Enhanced Cell Division Is Required for the Generation of Memory CD4 T Cells to Migrate Into Their Proper Location

CD4 T cell memory is fundamental for long-lasting immunity and effective secondary responses following infection or vaccination. We have previously found that memory CD4 T cells specific for systemic antigens preferentially reside in the bone marrow (BM) and arise from splenic CD49b⁺T-bet⁺ CD4 T cells. However, how BM-homing memory precursors are generated during an immune reaction is unknown. We show here that BM memory precursors are generated via augmented rates of cell division throughout a primary immune response. Treatment with the cytostatic drug cyclophosphamide or blockade of the CD28/B7 co-stimulatory pathway at the beginning of the contraction phase abrogates the generation of BM memory precursors. We determine that, following a critical number of cell divisions, memory precursors downregulate CCR7 and upregulate IL-2Rβ, indicating that loss of CCR7 and gain of IL-2 signal are required for the migration of memory precursors toward the BM.

Alpha2beta1 Integrin (VLA-2) Protects Activated Human Effector T Cells From Methotrexate-Induced Apoptosis

β1 integrins are critical for T cell migration, survival and costimulation. The integrin α2β1, which is a receptor for collagen, also named VLA-2, is a major costimulatory pathway of effector T cells and has been implicated in arthritis pathogenesis. Herein, we have examined its ability to promote methotrexate (MTX) resistance by enhancing effector T cells survival. Our results show that attachment of anti-CD3-activated human polarized Th17 cells to collagen but not to fibronectin or laminin led to a significant reduction of MTX-induced apoptosis. The anti-CD3+collagen-rescued cells still produce significant amounts of IL-17 and IFNγ upon their reactivation indicating that their inflammatory nature is preserved. Mechanistically, we found that the prosurvival role of anti-CD3+collagen involves activation of the MTX transporter ABCC1 (ATP Binding Cassette subfamily C Member 1). Finally, the protective effect of collagen/α2β1 integrin on MTX-induced apoptosis also occurs in memory CD4⁺ T cells isolated from rheumatoid arthritis (RA) patients suggesting its clinical relevance. Together these results show that α2β1 integrin promotes MTX resistance of effector T cells, and suggest that it could contribute to the development of MTX resistance that is seen in RA.

B Cells Negatively Regulate the Establishment of CD49b(+)T-bet(+) Resting Memory T Helper Cells in the Bone Marrow

During an immune reaction, some antigen-experienced CD4 T cells relocate from secondary lymphoid organs (SLOs) to the bone marrow (BM) in a CD49b-dependent manner and reside and rest there as professional memory CD4 T cells. However, it remains unclear how the precursors of BM memory CD4 T cells are generated in the SLOs. While several studies have so far shown that B cell depletion reduces the persistence of memory CD4 T cells in the spleen, we here show that B cell depletion enhances the establishment of memory CD4 T cells in the BM and that B cell transfer conversely suppresses it. Interestingly, the number of antigen-experienced CD4 T cells in the BM synchronizes the number of CD49b⁺T-bet⁺ antigen-experienced CD4 T cells in the spleen. CD49b⁺T-bet⁺ antigen-experienced CD4 T cells preferentially localize in the red pulp area of the spleen and the BM in a T-bet-independent manner. We suggest that B cells negatively control the generation of CD49b⁺T-bet⁺ precursors of resting memory CD4 T cells in the spleen and may play a role in bifurcation of activated effector and resting memory CD4 T cell lineages.

α2β1 Integrin

The α2β1 integrin, also known as VLA-2, GPIa-IIa, CD49b, was first identified as an extracellular matrix receptor for collagens and/or laminins [55, 56]. It is now recognized that the α2β1 integrin serves as a receptor for many matrix and nonmatrix molecules [35, 79, 128]. Extensive analyses have clearly elucidated the α2 I domain structural motifs required for ligand binding, and also defined distinct conformations that lead to inactive, partially active or highly active ligand binding [3, 37, 66, 123, 136, 137, 140]. The mechanisms by which the α2β1 integrin plays a critical role in platelet function and homeostasis have been carefully defined via in vitro and in vivo experiments [76, 104, 117, 125]. Genetic and epidemiologic studies have confirmed human physiology and disease states mediated by this receptor in immunity, cancer, and development [6, 20, 21, 32, 43, 90]. The role of the α2β1 integrin in these multiple complex biologic processes will be discussed in the chapter.

CD11a polymorphisms regulate TH2 cell homing and TH2-related disease

BACKGROUND

TH2-dependent diseases vary in severity according to genotype, but relevant gene polymorphisms remain largely unknown. The integrin CD11a is a critical determinant of allergic responses, and allelic variants of this gene might influence allergic phenotypes.

OBJECTIVE

We sought to determine major CD11a allelic variants in mice and human subjects and their importance to allergic disease expression.

METHODS

We sequenced mouse CD11a alleles from C57BL/6 and BALB/c strains to identify major polymorphisms; human CD11a single nucleotide polymorphisms were compared with allergic disease phenotypes as part of the international HapMap project. Mice on a BALB/c or C57BL/6 background and congenic for the other strain's CD11a allele were created to determine the importance of mouse CD11a polymorphisms in vivo and in vitro.

RESULTS

Compared with the C57BL/6 allele, the BALB/c CD11a allele contained a nonsynonymous change from asparagine to aspartic acid within the metal ion binding domain. In general, the BALB/c CD11a allele enhanced and the C57BL/6 CD11a allele suppressed TH2 cell-dependent disease caused by the parasite Leishmania major and allergic lung disease caused by the fungus Aspergillus niger. Relative to the C57BL/6 CD11a allele, the BALB/c CD11a allele conferred both greater T-cell adhesion to CD54 in vitro and enhanced TH2 cell homing to lungs in vivo. We further identified a human CD11a polymorphism that significantly associated with atopic disease and relevant allergic indices.

CONCLUSIONS

Polymorphisms in CD11a critically influence TH2 cell homing and diverse TH2-dependent immunopathologic states in mice and potentially influence the expression of human allergic disease.

Loss of the α2β1 integrin alters human papilloma virus-induced squamous carcinoma progression in vivo and in vitro

Expression of the α2β1 integrin, a receptor for collagens and laminin, is altered during tumor progression. Recent studies have linked polymorphisms in the α2 integrin gene with oral, squamous cell carcinoma (SCC). To determine the α2β1 integrin's role in SCC progression, we crossed α2-null mice with K14-HPV16 transgenic animals. Pathological progression to invasive carcinoma was evaluated in HPV-positive, α2-null (HPV/KO) and HPV-positive, wild-type (HPV/WT) animals. α2β1 integrin expression stimulated progression from hyperplasia and papillomatosis to dysplasia with concomitant dermal mast cell infiltration. Moreover, lymph node metastasis was decreased by 31.3% in HPV/KO, compared to HPV/WT, animals. To evaluate the integrin-specific impact on the malignant epithelium versus the microenvironment, we developed primary tumor cell lines. Although transition from dysplasia to carcinoma was unaltered during spontaneous tumor development, isolated primary HPV/KO SCC cell lines demonstrated decreased migration and invasion, compared to HPV/WT cells. When HPV/WT and HPV/KO SCC cells were orthotopically injected into WT or KO hosts, tumor α2β1 integrin expression resulted in decreased tumor latency, regardless of host integrin status. HPV/WT SCC lines failed to demonstrate a proliferative advantage in vitro, however, the HPV/WT tumors demonstrated increased growth compared to HPV/KO SCC lines in vivo. Although contributions of the integrin to the microenvironment cannot be excluded, our studies indicate that α2β1 integrin expression by HPV-transformed keratinocytes modulates SCC growth and progression.

An unexpected twist in alopecia areata pathogenesis: are NK cells protective and CD49b+ T cells pathogenic?

Natural killer (NK) cells have become a recent focus of interest in alopecia areata (AA) research. To further investigate their role in an established mouse model of AA, lesional skin from older C3H/HeJ mice with AA was grafted to young C3H/HeJ female mice, and NK cells were depleted by continuous administration of rabbit anti-asialo GM1. As expected, this significantly reduced the number of pure NK cells in murine skin, as assessed by NKp46 quantitative immunohistochemistry. Quite unexpectedly, however, the onset of hair loss in C3H/HeJ mice was accelerated, rather than retarded. NK cell depletion was accompanied by a significant increase in the number of perifollicular CD49b+T cells in the alopecic skin of anti-asialo GM1-treated mice. These findings underscore the need to carefully distinguish in future AA research between pure NK cells and defined subsets of CD49b+ lymphocytes, as they may exert diametrically opposed functions in hair follicle immunology and immunopathology.

Alpha2beta1 integrin is the major collagen-binding integrin expressed on human Th17 cells

Growing evidence indicates that collagen-binding integrins are important costimulatory molecules of effector T cells. In this study, we demonstrate that the major collagen-binding integrin expressed by human Th17 cells is alpha2beta1 (α2β1) or VLA-2, also known as the receptor for collagen I on T cells. Our results show that human naïve CD4(+) T cells cultured under Th17 polarization conditions preferentially upregulate α2β1 integrin rather than α1β1 integrin, which is the receptor for collagen IV on T cells. Double staining analysis for integrin receptors and intracellular IL-17 showed that α2 integrin but not α1 integrin is associated with Th17 cells. Cell adhesion experiments demonstrated that Th17 cells attach to collagen I and collagen II using α2β1 integrin but did not attach to collagen IV. Functional studies revealed that collagens I and II but not collagen IV costimulate the production of IL-17A, IL-17F and IFN-γ by human Th17 cells activated with anti-CD3. These results identify α2β1 integrin as the major collagen receptor expressed on human Th17 cells and suggest that it can be an important costimulatory molecule of Th17 cell responses.

IL-4 inhibits VLA-4 expression on Tc1 cells resulting in poor tumor infiltration and reduced therapy benefit

We and others have previously demonstrated that IL-4-dependent Tc2 are inferior to Tc1-effector CD8+ T cells in regulating tumor progression in vivo. This functional disparity relates, in part, to the comparatively poor ability of Tc2 to migrate into diseased tissues. We now show that IL-4 treatment of committed Tc1 cells promotes the selective loss in the expression of very-late antigen (VLA)-4, without impacting the Tc1 cytokine production profile, cytotoxic activity, or expression of alternate cell surface markers. Down-regulation of VLA-4 expression on Tc1 cells was unique to treatment with IL-4 (i.e. Tc1IL-4) and did not occur in the presence of the Type-2 cytokine IL-13 or the regulatory cytokines IL-10 or TGF-beta. Notably, the inhibitory effects of IL-4 on Tc1 expression of VLA-4 could be blocked by the presence of IL-12, but not IFN-gamma. Predictably, Tc1IL-4 (but not Tc1 control) cells adhere poorly to plate-bound VCAM-1-Fc fusion protein and fail to be co-stimulated by VCAM-1 in vitro. They were also markedly impaired in their ability to traffic into intracranial melanoma lesions after adoptive transfer, yielding inferior therapeutic benefit to tumor-bearing mice. These results suggest a novel suppressive mechanism for IL-4 that limits Tc1 efficacy via preventing their recruitment into tumors.

Developmental control of integrin expression regulates Th2 effector homing

Integrin CD18, a component of the LFA-1 complex that also includes CD11a, is essential for Th2, but not Th1, cell homing, but the explanation for this phenomenon remains obscure. In this study, we investigate the mechanism by which Th2 effector responses require the LFA-1 complex. CD11a-deficient T cells showed normal in vitro differentiation and function. However, Th2 cell-dependent allergic lung disease was markedly reduced in CD11a null mice and wild-type mice given LFA-1 inhibitors, whereas control of infection with Leishmania major, a Th1-dependent response, was enhanced. In both disease models, recruitment of IL-4-, but not IFN-gamma-secreting cells to relevant organs was impaired, as was adhesion of Th2 cells in vitro. These diverse findings were explained by the markedly reduced expression of CD29, an alternate homing integrin, on Th2, but not Th1, cells, which precludes Th2 homing in the absence of CD11a. Thus, murine Th1 and Th2 cells use distinct integrins for homing, suggesting novel opportunities for integrin-based therapeutic intervention in diverse human ailments influenced by Th2 cells.

Crosstalk between the alpha2beta1 integrin and c-met/HGF-R regulates innate immunity

Data from several investigators suggest that the alpha2beta1 integrin, a receptor for collagens, laminins, decorin, E-cadherin, matrix metalloproteinase-1, endorepellin, and several viruses, is required for innate immunity and regulation of autoimmune/allergic disorders. We demonstrated that the innate immune response to Listeria monocytogenes required alpha2beta1 integrin expression by peritoneal mast cells (PMCs). Ligation of the alpha2beta1 integrin by C1q contained in immune complexes comprised of Listeria and antibody was required for PMC activation in vitro and in vivo. However, ligation of the alpha2beta1 integrin alone was insufficient to activate cytokine secretion, suggesting that one or more additional signals emanating from a coreceptor were required for PMC activation. Here, we demonstrate that C1q, but neither other complement proteins nor FcRgamma, is required for early innate immune response to Listeria. The binding of Listeria's Internalin B (InlB) to hepatocyte growth factor receptor (HGF-R)/c-met provides the costimulatory function required for PMC activation. Either HGF or Listeria InlB bound to c-met and either C1q or type I collagen bound to alpha2beta1 integrin stimulates PMC activation. These findings suggest that crosstalk between c-met and the alpha2beta1 integrin may contribute to mast-cell activation in autoimmune and inflammatory disorders.

Preferential expression of very late antigen-4 on type 1 CTL cells plays a critical role in trafficking into central nervous system tumors

We have previously shown preferential tumor-homing and therapeutic efficacy of adoptively transferred type 1 CTL (Tc1) when compared with type 2 CTL (Tc2) in mice bearing intracranial ovalbumin-transfected melanoma (M05). Further characterizing the expression of a panel of homing receptors on Tc1 and Tc2 cells, we found that very late antigen (VLA)-4 (a heterodimer of CD49d and CD29), but none of other receptors evaluated, was expressed at significantly higher levels on Tc1 cells than on Tc2 cells. Although CD49d (alpha(4) integrin) can form heterodimers with both beta(1) (CD29) and beta(7) integrins, alpha(4)beta(7) complexes were not expressed by either Tc1 or Tc2 cells, suggesting that CD49d is solely expressed in VLA-4 complexes. VLA-4 expression on Tc2 cells was down-regulated in an interleukin (IL)-4 dose-dependent manner but not by other type 2 cytokines, such as IL-10 and IL-13, suggesting that IL-4 uniquely down-regulates VLA-4 expression on these cells. In accordance with the differential expression of VLA-4 on Tc1 versus Tc2 cells, Tc1 cells alone were competent to adhere to plate-bound VCAM-1-Ig fusion protein. Finally, the efficient trafficking of Tc1 cells into intracranial M05 lesions in vivo was efficiently blocked by administration of monoclonal antibodies against CD49d or VCAM-1 or small interfering RNA-mediated silencing of CD49d on Tc1 cells. Collectively, these data support the critical role of VLA-4 in the effective intracranial tumor homing of adoptive-transferred, antigen-specific Tc1 cells and suggest that more effective vaccine and/or ex vivo T-cell activation regimens may be developed by promoting the generation of VLA-4(+) antitumor Tc1 cells.

Collagen distribution and expression of collagen-binding alpha1beta1 (VLA-1) and alpha2beta1 (VLA-2) integrins on CD4 and CD8 T cells during influenza infection

Most viral infections occur in extralymphoid tissues, yet the mechanisms that regulate lymphocytes in these environments are poorly understood. One feature common to many extralymphoid environments is an abundance of extracellular matrix. We have studied the expression of two members of the beta(1) integrin family of collagen-binding receptors, alpha(1)beta(1) and alpha(2)beta(1) (CD49a, VLA-1 and CD49b, VLA-2, respectively), on CD4 and CD8 T cells during the response to influenza infection in the lung. Flow cytometry showed that whereas T cells infiltrating the lung and airways can express both CD49a and CD49b, CD49a expression was most strongly associated with the CD8+ subset. Conversely, though fewer CD4+ T cells expressed CD49a, most CD4+ cells in the lung tissue or airways expressed CD49b. This reciprocal pattern suggested that CD4 and CD8 T cells might localize differently within the lung tissue and this was supported by immunofluorescent analysis. CD8+ cells tended to localize in close proximity to the collagen IV-rich basement membranes of either the airways or blood vessels, whereas CD4+ cells tended to localize in the collagen I-rich interstitial spaces, with few in the airways. These observations suggest that CD4 T cell interaction with the tissue microenvironment is distinct from CD8 T cells and support the concept that CD4+ T cells in peripheral tissues are regulated differently than the CD8 subset.

Alpha2 beta1 integrin signaling augments T cell receptor-dependent production of interferon-gamma in human T cells

The mechanisms by which beta1 integrins modulate T cell costimulation are still poorly defined. In this study, we examined the role of collagen-binding integrins alpha1 beta1 and alpha2 beta1 in the regulation of interferon-gamma (IFN-gamma). We demonstrated that ligation of alpha2 beta1 integrin with Collagen type I (Coll I) but not alpha1 beta1 integrin with Collagen IV (Coll IV) significantly augmented T cell receptor (TCR)-dependent expression and production of IFN-gamma by effector T cells. The effect of Coll I was not due to cell adhesion as soluble Coll I also augmented TCR-dependent production of IFN-gamma. Inhibition studies indicated that activation of ERK and JNK MAPKs and PI3K/AKT are necessary for both TCR- and TCR+alpha2 beta1 integrin-dependent IFN-gamma production and that Coll I increases TCR-dependent activation of ERK and JNK MAPKs, and AKT. In addition, our results showed that Coll IV is less potent than Coll I in augmenting TCR-dependent activation of JNK/MAPK, which may explain the differential effect of collagen matrices on TCR-dependent IFN-gamma production. Together, these results indicate that the costimulatory effect of Coll I on IFN-gamma expression is integrated at the levels of ERK and JNK MAPKs and PI3K/AKT signaling pathways and suggest JNK/MAPK as a major signaling pathway of Coll I costimulation. Thus, our study identifies alpha2 beta1 integrin as an important regulatory pathway of IFN-gamma expression and provides novel insights into the signaling mechanisms of integrin costimulation in T cells. As such, this study further supports the functional importance that Coll I interactions may have on the control of T cell-dependent Th1 inflammatory diseases.

Functional specialization of memory Th cells revealed by expression of integrin CD49b

Infection or immunization induces heterogeneous memory T cell subsets, but their origin and protective value against infection are unclear. In this study, we report the functional characterization of two memory Th subsets, defined by expression of integrin CD49b. Stable CD49b expression is induced in up to one-half of all memory Th cells. More importantly, the CD49b- and CD49b+ subsets display distinct helper activities, typified by the production of IL-10 and TNF-alpha, respectively. Although the inflammatory properties of the CD49b+ subset are protective against intracellular bacterial infection, they are associated with immunopathology in acute viral infection. Modulation of the CD49b-defined memory Th subsets may provide infection type-specific interventions, where either enhancement of the inflammatory response or reduction of immunopathology is essential.

Collagen type I signaling reduces the expression and the function of human receptor activator of nuclear factor-kappa B ligand (RANKL) in T lymphocytes

The mechanisms by which beta1 integrins modulate T cell functions are still poorly defined. We have previously reported that signaling via the collagen type I (Coll I) receptor, alpha2beta1 integrin, inhibited FasL expression and protected Jurkat T cells from activation-induced cell death (AICD). In this study, we examined whether Coll I signaling in T cells also modulates the expression of the human receptor activator of nuclear factor-kappaB ligand (RANKL), a recently identified TNF family member which has important functions in osteoclastogenesis, cell survival and apoptosis. Our results show that in both Jurkat T cells and human primary T cells, Coll I signaling significantly reduces activation-induced RANKL expression by 50-60%. We also found that RANKL is not involved in AICD but participates in doxorubicin-induced apoptosis of leukemia T cell lines including Jurkat, CEM and HSB-2. In this respect, Coll I protected leukemia T cell lines from doxorubicin-induced apoptosis by inhibiting doxorubicin-induced RANKL expression. Together, our results suggest that by limiting the production of RANKL, Coll I signaling may contribute to the resistance of leukemia T cells to chemotherapy. Our study also emphasizes the importance Coll I signaling may have in the control of RANKL-associated T cell functions.

NKG2A and CD56 are coexpressed on activated TH2 but not TH1 lymphocytes

NKG2A is commonly expressed on cytotoxic cells but has been found on activated T helper (TH) cells. In identifying novel markers differentiating between TH1 and TH2 lymphocytes, we focused on NKG2A expression. TH1 and TH2 cells were negatively isolated from healthy volunteers for microarray analysis and reverse transcription polymerase chain reaction (RT-PCR). Flow cytometry of quiescent and activated TH1 and TH2 cells was performed. Isolates were >95% pure CD3+CD4+ cells (TH1=90.3% and TH2=84.1%). Microarrays revealed differential expression of NKG2A and NKG2C isoforms between TH1 and TH2 cells. RT-PCR indicated greater expression of NKG2A in TH2 cells (4-fold) and NKG2C in TH1 cells (3-fold). Flow studies revealed tripling of TH2 NKG2A with activation to 10.76+/-4.01% (p=0.05), a 23-fold increase in CD56 to 35+/-14.54% (p=0.03), and an increase in NKG2A+CD56+ double-positive cells to 3.04+/-1.38% (p=0.04). TH1 lymphocytes did not differ with activation. We identified co-induction of NKG2A and CD56 on activation of TH2 cells. These cells would likely bind more HLA-E and exhibit increased effector inhibition. Given that certain viruses are known to decrease MHC class I and thus HLA-E production by antigen-presenting cells, activated TH2 cells would bind less HLA-E in this scenario. This would likely result in less effector inhibition and a relatively robust TH2 response.

Collagen type I-mediated activation of ERK/MAP Kinase is dependent on Ras, Raf-1 and protein phosphatase 2A in Jurkat T cells

Growing evidence indicates that interactions of T cells with extracellular matrix through beta1 integrins are important for the regulation of T cell-mediated immune responses and diseases. In this regard, we have recently demonstrated that collagen I (Coll I) through alpha2beta1 integrin inhibited Fas-induced apoptosis of T cells by activating a protein phosphatase 2A (PP2A)-dependent ERK/MAP Kinase pathway. As survival of T cells is critical for their functions, we further investigated the mechanisms underlying the activation of this pathway. Inhibition studies demonstrated that Coll I activates the ERK/MAP Kinase pathway in Jurkat T cells through the activation of Ras and Raf-1. Activation of PP2A was not necessary for the binding of Coll I to Jurkat T cells, but is required for the activation of Raf-1. In accordance, activation of Ras, Raf-1 and PP2A were also required for the ability of Coll I to protect Jurkat T cells from Fas-induced apoptosis. In contrast and despite its capacity to activate Ras, fibronectin (Fbn) failed to activate PP2A and Raf-1. These results might explain, at least in part, the weak ability of Fbn to activate ERK in T cells, supporting thus the differential signaling of beta1 integrin members in these cells. This study provides novel insights into the mechanisms by which beta1 integrins activate the ERK/MAP Kinase pathway in T cells, and is the first report to provide a role for PP2A in integrin-mediated ERK/MAP Kinase activation.

Hypervariable genes--experimental error or hidden dynamics

In a homogeneous group of samples, not all genes of high variability stem from experimental errors in microarray experiments. These expression variations can be attributed to many factors including natural biological oscillations or metabolic processes. The behavior of these genes can tease out important clues about naturally occurring dynamic processes in the organism or experimental system under study. We developed a statistical procedure for the selection of genes with high variability denoted hypervariable (HV) genes. After the exclusion of low expressed genes and a stabilizing log-transformation, the majority of genes have comparable residual variability. Based on an F-test, HV genes are selected as having a statistically significant difference from the majority of variability stabilized genes measured by the 'reference group'. A novel F-test clustering technique, further noted as 'F-means clustering', groups HV genes with similar variability patterns, presumably from their participation in a common dynamic biological process. F-means clustering establishes, for the first time, groups of co-expressed HV genes and is illustrated with microarray data from patients with juvenile rheumatoid arthritis and healthy controls.

Differential requirement for CD18 in T-helper effector homing

To understand the integrin requirements of T-helper (T(H)) effector subsets, we investigated the contribution of CD18 (beta(2) integrin) to T(H)1 and T(H)2 function in vitro and in relevant disease models. CD18-deficient (Itgb2(-/-)) T cells showed largely normal in vitro function. Compared with wild-type mice, Itgb2(-/-) mice were better able to resolve Leishmania major infection and generated a superior T(H)1 immune response, as assessed from draining lymph nodes. In contrast, T(H)2-dependent allergic lung disease was markedly impaired in mutant mice. In both models, development of T(H)1 and T(H)2 cells in spleens was normal, but accumulation of T(H)2 (not T(H)1) cells at inflammatory sites was reduced. Thus, CD18 is selectively required for T(H)2, but not T(H)1, homing and has a minimal influence on T-effector development. These findings suggest a new integrin-based therapeutic approach in which the outcomes of diverse diseases may be favorably influenced by altering the homing of T(H)2 cells.