Strong alpha beta and gamma delta TCR response in a patient with disseminated Mycobacterium avium infection and lack of NK cells and monocytopenia

Innate and Adaptive Lymphocytes in Non-Tuberculous Mycobacteria Lung Disease: A Review

Non-tuberculous mycobacteria (NTM) are ubiquitous environmental microorganisms capable of a wide range of infections that primarily involve the lymphatic system and the lower respiratory tract. In recent years, cases of lung infection sustained by NTM have been steadily increasing, due mainly to the ageing of the population with underlying lung disease, the enlargement of the cohort of patients undergoing immunosuppressive medications and the improvement in microbiologic diagnostic techniques. However, only a small proportion of individuals at risk ultimately develop the disease due to reasons that are not fully understood. A better understanding of the pathophysiology of NTM pulmonary disease is the key to the development of better diagnostic tools and therapeutic targets for anti-mycobacterial therapy. In this review, we cover the various types of interactions between NTM and lymphoid effectors of innate and adaptive immunity. We also give a brief look into the mechanism of immune exhaustion, a phenomenon of immune dysfunction originally reported for chronic viral infections and cancer, but recently also observed in the setting of mycobacterial diseases. We try to set the scene to postulate that a better knowledge of immune exhaustion can play a crucial role in establishing prognostic/predictive factors and enabling a broader investigation of immune-modulatory drugs in the experimental treatment of NTM pulmonary disease.

Protective role of natural killer cells in neuropathic pain conditions

ABSTRACT

During the past few years, the research of chronic neuropathic pain has focused on neuroinflammation within the central nervous system and its impact on pain chronicity. As part of the ERA-Net NEURON consortium, we aimed to identify immune cell patterns in the cerebrospinal fluid (CSF) of patients with herpes zoster neuralgia and patients with polyneuropathy (PNP), which may contribute to pain chronicity in these neuropathic pain conditions. Cerebrospinal fluid of 41 patients (10 herpes zoster and 31 PNP) was analyzed by flow cytometry identifying lymphocyte subsets: CD4+ (T-helper cells), CD8+ (cytotoxic T cells), CD19+ (B cells), and CD56+ (natural killer [NK]) cells. At baseline and at follow-up, the somatosensory phenotype was assessed with quantitative sensory testing. In addition, the patients answered epidemiological questionnaires and the PainDETECT questionnaire. Immune cell profiles and somatosensory profiles, as well as painDETECT questionnaire scores, were analyzed and correlated to determine specific immune cell patterns, which contribute to chronic pain. We found a negative correlation (P = 0.004, r = -0.596) between the frequency of NK cells and mechanical pain sensitivity (MPS), one of the most relevant quantitative sensory testing markers for central sensitization; a high frequency of NK cells correlated with low MPS. The analysis of the individual follow-up showed a worsening of the pain condition if NK-cell frequency was low. Low NK-cell frequency is associated with signs of central sensitization (MPS), whereas high NK-cell frequency might prevent central sensitization. Therefore, NK cells seem to play a protective role within the neuroinflammatory cascade and may be used as a marker for pain chronicity.

Manipulation of the Innate Immune Response by Varicella Zoster Virus

Varicella zoster virus (VZV) is the causative agent of chickenpox (varicella) and shingles (herpes zoster). VZV and other members of the herpesvirus family are distinguished by their ability to establish a latent infection, with the potential to reactivate and spread virus to other susceptible individuals. This lifelong relationship continually subjects VZV to the host immune system and as such VZV has evolved a plethora of strategies to evade and manipulate the immune response. This review will focus on our current understanding of the innate anti-viral control mechanisms faced by VZV. We will also discuss the diverse array of strategies employed by VZV to regulate these innate immune responses and highlight new knowledge on the interactions between VZV and human innate immune cells.

Functional paralysis of human natural killer cells by alphaherpesviruses

Natural killer (NK) cells are implicated as important anti-viral immune effectors in varicella zoster virus (VZV) infection. VZV can productively infect human NK cells, yet it is unknown how, or if, VZV can directly affect NK cell function. Here we demonstrate that VZV potently impairs the ability of NK cells to respond to target cell stimulation in vitro, leading to a loss of both cytotoxic and cytokine responses. Remarkably, not only were VZV infected NK cells affected, but VZV antigen negative NK cells that were exposed to virus in culture were also inhibited. This powerful impairment of function was dependent on direct contact between NK cells and VZV infected inoculum cells. Profiling of the NK cell surface receptor phenotype by multiparameter flow cytometry revealed that functional receptor expression is predominantly stable. Furthermore, inhibited NK cells were still capable of releasing cytotoxic granules when the stimulation signal bypassed receptor/ligand interactions and early signalling, suggesting that VZV paralyses NK cells from responding. Phosflow examination of key components in the degranulation signalling cascade also demonstrated perturbation following culture with VZV. In addition to inhibiting degranulation, IFN-γ and TNF production were also repressed by VZV co-culture, which was most strongly regulated in VZV infected NK cells. Interestingly, the closely related virus, herpes simplex virus type 1 (HSV-1), was also capable of efficiently infecting NK cells in a cell-associated manner, and demonstrated a similar capacity to render NK cells unresponsive to target cell stimulation–however HSV-1 differentially targeted cytokine production compared to VZV. Our findings progress a growing understanding of pathogen inhibition of NK cell function, and reveal a previously unreported strategy for VZV to manipulate the immune response.

Natural killer (NK) cells–as their name implies–are the immune system’s ready to respond ‘killers’, being able to help control viral infection by cytolytic killing of infected cells and secretion of pro-inflammatory cytokines to activate and direct the immune response. In retaliation, viruses like varicella zoster virus (VZV; the cause of chickenpox and shingles) work to dampen the immune system in order to establish infection in human hosts. We have identified a previously uncharacterised ability of VZV to render NK cells unresponsive to target cells, hindering NK cells from both cytotoxic function and cytokine production. NK cells still maintained predominantly stable expression of functional surface receptors, and were capable of releasing cytotoxic granules when given a receptor-independent stimulus. In this way, VZV paralyses NK cells from functionally responding to target cells, essentially taking the ‘killer’ out of natural killer cells.

Varicella zoster virus productively infects human peripheral blood mononuclear cells to modulate expression of immunoinhibitory proteins and blocking PD-L1 enhances virus-specific CD8+ T cell effector function

Varicella zoster virus (VZV) is a lymphotropic alpha-herpesvirinae subfamily member that produces varicella on primary infection and causes zoster, vascular disease and vision loss upon reactivation from latency. VZV-infected peripheral blood mononuclear cells (PBMCs) disseminate virus to distal organs to produce clinical disease. To assess immune evasion strategies elicited by VZV that may contribute to dissemination of infection, human PBMCs and VZV-specific CD8+ T cells (V-CD8+) were mock- or VZV-infected and analyzed for immunoinhibitory protein PD-1, PD-L1, PD-L2, CTLA-4, LAG-3 and TIM-3 expression using flow cytometry. All VZV-infected PBMCs (monocytes, NK, NKT, B cells, CD4+ and CD8+ T cells) and V-CD8+ showed significant elevations in PD-L1 expression compared to uninfected cells. VZV induced PD-L2 expression in B cells and V-CD8+. Only VZV-infected CD8+ T cells, NKT cells and V-CD8+ upregulated PD-1 expression, the immunoinhibitory receptor for PD-L1/PD-L2. VZV induced CTLA-4 expression only in V-CD8+ and no significant changes in LAG-3 or TIM-3 expression were observed in V-CD8+ or PBMC T cells. To test whether PD-L1, PD-L2 or CTLA-4 regulates V-CD8+ effector function, autologous PBMCs were VZV-infected and co-cultured with V-CD8+ cells in the presence of blocking antibodies against PD-L1, PD-L2 or CTLA-4; ELISAs revealed significant elevations in IFNγ only upon blocking of PD-L1. Together, these results identified additional immune cells that are permissive to VZV infection (monocytes, B cells and NKT cells); along with a novel mechanism for inhibiting CD8+ T cell effector function through induction of PD-L1 expression.

Emerging insights into human health and NK cell biology from the study of NK cell deficiencies

Human NK cells are innate immune effectors that play a critical roles in the control of viral infection and malignancy. The importance of their homeostasis and function can be demonstrated by the study of patients with primary immunodeficiencies (PIDs), which are part of the family of diseases known as inborn defects of immunity. While NK cells are affected in many PIDs in ways that may contribute to a patient's clinical phenotype, a small number of PIDs have an NK cell abnormality as their major immunological defect. These PIDs can be collectively referred to as NK cell deficiency (NKD) disorders and include effects upon NK cell numbers, subsets, and/or functions. The clinical impact of NKD can be severe including fatal viral infection, with particular susceptibility to herpesviral infections, such as cytomegalovirus, varicella zoster virus, and Epstein-Barr virus. While NKD is rare, studies of these diseases are important for defining specific requirements for human NK cell development and homeostasis. New themes in NK cell biology are emerging through the study of both known and novel NKD, particularly those affecting cell cycle and DNA damage repair, as well as broader PIDs having substantive impact upon NK cells. In addition, the discovery of NKD that affects other innate lymphoid cell (ILC) subsets opens new doors for better understanding the relationship between conventional NK cells and other ILC subsets. Here, we describe the biology underlying human NKD, particularly in the context of new insights into innate immune cell function, including a discussion of recently described NKD with accompanying effects on ILC subsets. Given the impact of these disorders upon human immunity with a common focus upon NK cells, the unifying message of a critical role for NK cells in human host defense singularly emerges.

Can immune biomarkers predict infections in solid organ transplant recipients? A review of current evidence

Despite improvements in graft survival, solid organ transplantation is still associated with considerable infection induced morbidity and mortality. If we were able to show that serious infection risk was associated with excessive suppression of immune capacity, we would be justified in "personalizing" the extent of immunosuppression by carefully monitored reduction to see if we can improve immune compromize without increasing the risk of rejection. Reliable biomarkers are needed to identify this patients at an increased risk of infection. This review focuses on the currently available evidence in solid organ transplant recipients for immune non-pathogen specific biomarkers to predict severe infections with the susceptibility to particular pathogens according to the component of the immune system that is suppressed. This review is categorized into immune biomarkers representative of the humoral, cellular, phagocytic, natural killer cell and complement system. Biomarkers humoral and cellular systems of the that have demonstrated an association with infections include immunoglobulins, lymphocyte number, lymphocyte subsets, intracellular concentrations of adenosine triphosphate in stimulated CD4⁺ cells and soluble CD30. Biomarkers of the innate immune system that have demonstrated an association with infections include natural killer cell numbers, complement and mannose binding lectin. Emerging evidence shows that quantification of viral nucleic acid (such as Epstein Barr Virus) can act as a biomarker to predict all-cause infections. Studies that show the most promise are those in which several immune biomarkers are assessed in combination. Ongoing research is required to validate non-pathogen specific immune biomarkers in multi-centre studies using standardized study designs.

Varicella zoster virus productively infects human natural killer cells and manipulates phenotype

Varicella zoster virus (VZV) is a ubiquitous human alphaherpesvirus, responsible for varicella upon primary infection and herpes zoster following reactivation from latency. To establish lifelong infection, VZV employs strategies to evade and manipulate the immune system to its advantage in disseminating virus. As innate lymphocytes, natural killer (NK) cells are part of the early immune response to infection, and have been implicated in controlling VZV infection in patients. Understanding of how VZV directly interacts with NK cells, however, has not been investigated in detail. In this study, we provide the first evidence that VZV is capable of infecting human NK cells from peripheral blood in vitro. VZV infection of NK cells is productive, supporting the full kinetic cascade of viral gene expression and producing new infectious virus which was transmitted to epithelial cells in culture. We determined by flow cytometry that NK cell infection with VZV was not only preferential for the mature CD56^dim NK cell subset, but also drove acquisition of the terminally-differentiated maturity marker CD57. Interpretation of high dimensional flow cytometry data with tSNE analysis revealed that culture of NK cells with VZV also induced a potent loss of expression of the low-affinity IgG Fc receptor CD16 on the cell surface. Notably, VZV infection of NK cells upregulated surface expression of chemokine receptors associated with trafficking to the skin –a crucial site in VZV disease where highly infectious lesions develop. We demonstrate that VZV actively manipulates the NK cell phenotype through productive infection, and propose a potential role for NK cells in VZV pathogenesis.

Varicella zoster virus (VZV) is a pervasive pathogen, causing chickenpox during primary infection and shingles when the virus reactivates from latency. VZV is therefore a lifelong infection for humans, warranting investigation of how this virus interacts with the immune system. One of the first immune cells to respond to viral infection are natural killer (NK) cells, yet little is known about how VZV interacts with NK cells. We demonstrate for the first time that VZV infects human blood NK cells and can use them to pass on infection to other cells in culture. Furthermore, VZV displays a predilection for infecting mature NK cells, and amplifies expression of receptors that would promote trafficking to the skin– the site of highly infectious lesions during chickenpox and shingles. Our findings suggest a role for NK cells in VZV disease and enhances our understanding of how lifelong infections interact with the human immune system.

Licensed and Unlicensed NK Cells: Differential Roles in Cancer and Viral Control

Natural killer (NK) cells are known for their well characterized ability to control viral infections and eliminate tumor cells. Through their repertoire of activating and inhibitory receptors, NK cells are able to survey different potential target cells for various surface markers, such as MHC-I – which signals to the NK cell that the target is healthy – as well as stress ligands or viral proteins, which alert the NK cell to the aberrant state of the target and initiate a response. According to the “licensing” hypothesis, interactions between self-specific MHC-I receptors – Ly49 in mice and KIR in humans – and self-MHC-I molecules during NK cell development is crucial for NK cell functionality. However, there also exists a large proportion of NK cells in mice and humans, which lack self-specific MHC-I receptors and are consequentially “unlicensed.” While the licensed NK cell subset plays a major role in the control of MHC-I-deficient tumors, this review will go on to highlight the important role of the unlicensed NK cell subset in the control of MHC-I-expressing tumors, as well as in viral control. Unlike the licensed NK cells, unlicensed NK cells seem to benefit from the lack of self-specific inhibitory receptors, which could otherwise be exploited by some aberrant cells for immunoevasion by upregulating the expression of ligands or mimic ligands for these receptors.

Varicella-Zoster Virus and Herpes Simplex Virus 1 Differentially Modulate NKG2D Ligand Expression during Productive Infection

Natural killer (NK) cell-deficient patients are particularly susceptible to severe infection with herpesviruses, especially varicella-zoster virus (VZV) and herpes simplex virus 1 (HSV-1). The critical role that NK cells play in controlling these infections denotes an intricate struggle for dominance between virus and NK cell antiviral immunity; however, research in this area has remained surprisingly limited. Our study addressed this absence of knowledge and found that infection with VZV was not associated with enhanced NK cell activation, suggesting that the virus uses specific mechanisms to limit NK cell activity. Analysis of viral regulation of ligands for NKG2D, a potent activating receptor ubiquitously expressed on NK cells, revealed that VZV differentially modulates expression of the NKG2D ligands MICA, ULBP2, and ULBP3 by upregulating MICA expression while reducing ULBP2 and ULBP3 expression on the surface of infected cells. Despite being closely related to VZV, infection with HSV-1 produced a remarkably different effect on NKG2D ligand expression. A significant decrease in MICA, ULBP2, and ULBP3 was observed with HSV-1 infection at a total cellular protein level, as well as on the cell surface. We also demonstrate that HSV-1 differentially regulates expression of an additional NKG2D ligand, ULBP1, by reducing cell surface expression while total protein levels are unchanged. Our findings illustrate both a striking point of difference between two closely related alphaherpesviruses, as well as suggest a powerful capacity for VZV and HSV-1 to evade antiviral NK cell activity through novel modulation of NKG2D ligand expression.

IMPORTANCE

Patients with deficiencies in NK cell function experience an extreme susceptibility to infection with herpesviruses, in particular, VZV and HSV-1. Despite this striking correlation, research into understanding how these two alphaherpesviruses interact with NK cells is surprisingly limited. Through examination of viral regulation of ligands to the activating NK cell receptor NKG2D, we reveal patterns of modulation by VZV, which were unexpectedly varied in response to regulation by HSV-1 infection. Our study begins to unravel the undoubtedly complex interactions that occur between NK cells and alphaherpesvirus infection by providing novel insights into how VZV and HSV-1 manipulate NKG2D ligand expression to modulate NK cell activity, while also illuminating a distinct variation between two closely related alphaherpesviruses.

Haematopoietic and immune defects associated with GATA2 mutation

Heterozygous familial or sporadic GATA2 mutations cause a multifaceted disorder, encompassing susceptibility to infection, pulmonary dysfunction, autoimmunity, lymphoedema and malignancy. Although often healthy in childhood, carriers of defective GATA2 alleles develop progressive loss of mononuclear cells (dendritic cells, monocytes, B and Natural Killer lymphocytes), elevated FLT3 ligand, and a 90% risk of clinical complications, including progression to myelodysplastic syndrome (MDS) by 60 years of age. Premature death may occur from childhood due to infection, pulmonary dysfunction, solid malignancy and MDS/acute myeloid leukaemia. GATA2 mutations include frameshifts, amino acid substitutions, insertions and deletions scattered throughout the gene but concentrated in the region encoding the two zinc finger domains. Mutations appear to cause haplo-insufficiency, which is known to impair haematopoietic stem cell survival in animal models. Management includes genetic counselling, prevention of infection, cancer surveillance, haematopoietic monitoring and, ultimately, stem cell transplantation upon the development of MDS or another life-threatening complication.

Natural killer cell deficiency

Natural killer (NK) cells are part of the innate immune defense against infection and cancer and are especially useful in combating certain viral pathogens. The utility of NK cells in human health has been underscored by a growing number of persons who are deficient in NK cells and/or their functions. This can be in the context of a broader genetically defined congenital immunodeficiency, of which there are more than 40 presently known to impair NK cells. However, the abnormality of NK cells in certain cases represents the majority immunologic defect. In aggregate, these conditions are termed NK cell deficiency. Recent advances have added clarity to this diagnosis and identified defects in 3 genes that can cause NK cell deficiency, as well as some of the underlying biology. Appropriate consideration of these diagnoses and patients raises the potential for rational therapeutic options and further innovation.

Mutations in GATA2 cause human NK cell deficiency with specific loss of the CD56(bright) subset

Mutations in the transcription factor GATA2 underlie the syndrome of monocytopenia and B- and natural killer (NK)-cell lymphopenia associated with opportunistic infections and cancers. In addition, patients have recurrent and severe viral infections. NK cells play a critical role in mediating antiviral immunity. Human NK cells are thought to mature in a linear fashion, with the CD56(bright) stage preceding terminal maturation to the CD56(dim) stage, considered the most enabled for cytotoxicity. Here we report an NK cell functional defect in GATA2-deficient patients and extend this genetic lesion to what is considered to be the original NK cell-deficient patient. In most cases, GATA2 deficiency is accompanied by a severe reduction in peripheral blood NK cells and marked functional impairment. The NK cells detected in peripheral blood of some GATA2-deficient patients are exclusively of the CD56(dim) subset, which is recapitulated on in vitro NK cell differentiation. In vivo, interferon α treatment increased NK cell number and partially restored function but did not correct the paucity of CD56(bright) cells. Thus, GATA2 is required for the maturation of human NK cells and the maintenance of the CD56(bright) pool in the periphery. Defects in GATA2 are a novel cause of profound NK cell dysfunction.

Sequential desensitization of CXCR4 and S1P5 controls natural killer cell trafficking

During development, natural killer (NK) cells exit the BM to reach the blood. CXCR4 retains NK cells in the BM, whereas the sphingosine-1 phosphate receptor 5 (S1P5) promotes their exit from this organ. However, how the action of these receptors is coordinated to preserve NK-cell development in the BM parenchyma while providing mature NK cells at the periphery is unclear. The role of CXCR4 and S1P5 in NK-cell recirculation at the periphery is also unknown. In the present study, we show that, during NK-cell differentiation, CXCR4 expression decreases whereas S1P5 expression increases, thus favoring the exit of mature NK cells via BM sinusoids. Using S1P5(-/-) mice and a new knockin mouse model in which CXCR4 cannot be desensitized (a mouse model of warts, hypogammaglobulinemia, infections, and myelokathexis [WHIM] syndrome), we demonstrate that NK-cell exit from the BM requires both CXCR4 desensitization and S1P5 engagement. These 2 signals occur independently of each other: CXCR4 desensitization is not induced by S1P5 engagement and vice versa. Once in the blood, the S1P concentration increases and S1P5 responsiveness decreases. This responsiveness is recovered in the lymph nodes to allow NK-cell exit via lymphatics in a CXCR4-independent manner. Therefore, coordinated changes in CXCR4 and S1P5 responsiveness govern NK-cell trafficking.

Autosomal dominant and sporadic monocytopenia with susceptibility to mycobacteria, fungi, papillomaviruses, and myelodysplasia

We identified 18 patients with the distinct clinical phenotype of susceptibility to disseminated nontuberculous mycobacterial infections, viral infections, especially with human papillomaviruses, and fungal infections, primarily histoplasmosis, and molds. This syndrome typically had its onset in adulthood (age range, 7-60 years; mean, 31.1 years; median, 32 years) and was characterized by profound circulating monocytopenia (mean, 13.3 cells/microL; median, 14.5 cells/microL), B lymphocytopenia (mean, 9.4 cells/microL; median, 4 cells/microL), and NK lymphocytopenia (mean, 16 cells/microL; median, 5.5 cells/microL). T lymphocytes were variably affected. Despite these peripheral cytopenias, all patients had macrophages and plasma cells at sites of inflammation and normal immunoglobulin levels. Ten of these patients developed 1 or more of the following malignancies: 9 myelodysplasia/leukemia, 1 vulvar carcinoma and metastatic melanoma, 1 cervical carcinoma, 1 Bowen disease of the vulva, and 1 multiple Epstein-Barr virus(+) leiomyosarcoma. Five patients developed pulmonary alveolar proteinosis without mutations in the granulocyte-macrophage colony-stimulating factor receptor or anti-granulocyte-macrophage colony-stimulating factor autoantibodies. Among these 18 patients, 5 families had 2 generations affected, suggesting autosomal dominant transmission as well as sporadic cases. This novel clinical syndrome links susceptibility to mycobacterial, viral, and fungal infections with malignancy and can be transmitted in an autosomal dominant pattern.

Human natural killer cell deficiencies

PURPOSE OF REVIEW

Human natural killer cell deficiencies are a relevant clinical entity that provides insight into the role of natural killer cells in host defense, as well as the basic biology of natural killer cells. Since previously reviewing these disorders, significant developments warrant their reconsideration.

RECENT FINDINGS

Human natural killer cell deficiencies can occur as part of a more pervasive immunodeficiency syndrome or, rarely, in isolation. The most informative examples of the former are in the context of a known genetic defect, because the deficiency of natural killer cell development or activity can be attributed to the specific gene function. Since last reviewed, there are five human gene mutations that are now appreciated to affect natural killer cells, and additional new insights into natural killer cell biology have been obtained through seven others. Six new reports of isolated natural killer cell deficiencies, as well as a suggested classification scheme, are also reviewed.

SUMMARY

Appreciation of human genetic syndromes that include natural killer cell deficiencies, as well as new cases of isolated natural killer cell deficiencies, continue to advance the understanding of natural killer cell biology and solidify the role of natural killer cells in defense against human herpesviral infection.

Familial NK cell deficiency associated with impaired IL-2- and IL-15-dependent survival of lymphocytes

We previously reported the clinical phenotype of two siblings with a novel inherited developmental and immunodeficiency syndrome consisting of severe intrauterine growth retardation and the impaired development of specific lymphoid lineages, including transient CD8 alphabeta T lymphopenia and a persistent lack of blood NK cells. We describe here the elucidation of a plausible underlying pathogenic mechanism, with a cellular phenotype of impaired survival of both fresh and herpesvirus saimiri-transformed T cells, in the surviving child. Clearly, NK cells could not be studied. However, peripheral blood T lymphocytes displayed excessive apoptosis ex vivo. Moreover, the survival rates of CD4 and CD8 alphabeta T cell blasts generated in vitro, and herpesvirus saimiri-transformed T cells cultured in vitro, were low, but not nil, following treatment with IL-2 and IL-15. In contrast, Fas-mediated activation-induced cell death was not enhanced, indicating a selective excess of cytokine deprivation-mediated apoptosis. In keeping with the known roles of IL-2 and IL-15 in the development of NK and CD8 T cells in the mouse model, these data suggest that an impaired, but not abolished, survival response to IL-2 and IL-15 accounts for the persistent lack of NK cells and the transient CD8 alphabeta T lymphopenia documented in vivo. Impaired cytokine-mediated lymphocyte survival is likely to be the pathogenic mechanism underlying this novel form of inherited and selective NK deficiency in humans.

Immune regulation of gammadelta T cell responses in mycobacterial infections

Antigen-specific gammadelta T cells may play a role in anti-mycobacterial immunity. Studies done in humans and animal models have demonstrated complex patterns of gammadelta T cell immune responses during early mycobacterial infections and chronic tuberculosis. Recent studies have also shown a clinical correlation between major recall expansion of antigen-specific gammadelta T cells and immunity against fatal early mycobacterial diseases. Multiple host and microbial factors can regulate diverse immune responses of phosphoantigen-specific gammadelta T cells during mycobacterial infections.

Human natural killer cell deficiencies and susceptibility to infection

There are a surprisingly large number of human natural killer (NK) cell deficiency states that provide insight into the role of NK cells in defense against human infectious disease. Many disorders associated with NK cell defects are caused by single gene mutations and, thus, give additional understanding concerning the function of specific molecules in NK cell development and activities. A resounding theme of NK cell deficiencies is susceptibility to herpesviruses, suggesting that unexplained severe herpesviral infection should raise the possibility of an NK cell deficit.

Viral evasion of natural killer cells

Viruses have evolved mechanisms to avoid the host immune system, including means of escaping detection by both the innate and adaptive immune responses. Natural killer (NK) cells are a central component of the innate immune system and are crucial in defense against certain viruses. To attain a state of chronic infection, some successful viruses have developed specific mechanisms to evade detection by and activation of NK cells. These NK cell-specific evasion mechanisms fall into distinct mechanistic categories used in numerous virus families.