HLA-C and Killer Cell Immunoglobulin-like Receptor Genes in Idiopathic Bronchiectasis

How does comorbid bronchiectasis affect asthmatic patients? A meta-analysis

OBJECTIVE

Asthma and bronchiectasis are known to be two distinct diseases with different etiology, pathophysiology, management, and prognosis. However, a high prevalence of bronchiectasis has been reported in patients with severe asthma. Thus, it is of great importance to identify the impact of bronchiectasis on asthmatic patients.Data sources: Databases including PubMed, Embase, Cochrane, Web of Science were searched comprehensively to identify relevant human clinical studies published until February 2020.Study selections: Two investigators (Gelei Lan and Guochao Shi) independently obtained the potentially eligible articles based on their titles and abstracts. When opinions differed between the investigators, discussions were made to reach an agreement. The authors of the included studies were contacted for inquiry when necessary.

RESULTS

Six observational studies with 1004 patients were included in the meta-analysis. The mean prevalence of bronchiectasis in patients with asthma was 35.2% (ranging from 2.2% to 47%). Asthmatic patients with bronchiectasis were older, had a longer disease duration, exhibited greater severity, and showed more frequent exacerbations and hospitalization, and poorer lung function, compared with the patients without bronchiectasis.

CONCLUSION

Despite of the heterogeneity between included studies and detectable publication bias, this meta-analysis demonstrated the impact of comorbid bronchiectasis on asthmatic patients. Thus, coexistence of bronchiectasis should be considered a clinical phenotype of asthma, which may have associations with exacerbation and hospitalization.

Killer cell immunoglobulin-like receptors (KIR) and human leukocyte antigen-C (HLA-C) allorecognition patterns in women with endometriosis

Endometriosis shares similarities with several autoimmune diseases. The human leukocyte antigen (HLA)-C genotype is associated with several human autoimmune diseases. HLA-C is a ligand of killer cell immunoglobulin receptors (KIRs) and is an essential regulator of natural killer cell activity, which is associated with endometriosis progression. Polymorphisms in HLA-C and KIR affect the activity of NK cells and susceptibility to several diseases. Therefore, we attempted to investigate an association between HLA-C genotype and KIR polymorphism and the occurrence of endometriosis. We tested the association of certain KIR and HLA-C combinations and the development of endometriosis by characterizing both KIR and HLA-C genes in 147 women with endometriosis and 117 controls. The HLA-C genotypes and KIR polymorphisms were analyzed via DNA-based method for higher-resolution genotyping. We found that the occurrence of HLA-C*03:03*01 was increased in endometriosis than in control groups. Analysis of various KIR haplotypes revealed differences between the endometriosis and control cohorts. The number of KIR centromeric A/A haplotypes was increased in the endometriosis group than controls. Moreover, the endometriosis cohort was characterized by reduced number of KIR2DS2-positive individuals in the Han Chinese population. Our current findings suggest that the KIR and HLA-C genotypes are associated with the pathogenesis of endometriosis.

Adaptive NKG2C+ natural killer cells are related to exacerbations and nutritional abnormalities in COPD patients

Abstract

Chronic obstructive pulmonary disease (COPD) is a chronic and often progressive disorder with a heterogeneous presentation and frequent systemic manifestations. Several aspects like persistence in smoking habit, continuous exacerbations, alpha-1-antitrypsin deficiency and inflammatory-immune response, are involved in the pathophysiology and progression of the disease. However, the role of natural killer (NK) cells remains controversial. Otherwise, human cytomegalovirus (HCMV) infection has been reported to induce an adaptive differentiation and expansion of an NK cell subset which carries the CD94/NKG2C receptor, which may contribute to an upset immune defense. For these reasons, our objective is to assess the distribution of NK cells and their subset in COPD patients and some of its phenotypes.

Methods

Peripheral blood samples were obtained from 66 COPD patients. HCMV serology and the proportions of total NK cells and the NKG2C+ and NKG2A+ subsets were evaluated by flow cytometry. The NKG2C genotype was also assessed.

Results

Eighty-eight per cent of COPD patients were HCMV(+), and the proportions of total NK cells were higher in patients with severe-very severe airway obstruction than in those with only mild-moderate involvement. There were no differences in the proportions of NKG2C+ cells between controls and COPD, either among COPD patients classified by severity of the disease. However, the percentage of NKG2C+ cells were higher in COPD patients with frequent exacerbations than in occasional exacerbators, and higher in cases with reduced lean mass (Fat free mass index) than in those with normal nutritional status.

Conclusion

These results suggest a relationship between levels of NKG2C+ cells in COPD patients and clinical variables closely linked to a poor/worse prognosis.

Chronic Bacterial Infection Prevalence, Risk Factors, and Characteristics: A Bronchiectasis Population-Based Prospective Study

BACKGROUND

Few data are available on chronic bacterial infections (CBI) in bronchiectasis patients. Given that CBI seems to trigger longer hospital stays, worse outcomes, and morbimortality, this study was undertaken to assess CBI prevalence, characteristics, and risk factors in outpatients with bronchiectasis.

METHODS

A total of 186 patients followed in a bronchiectasis tertiary referral centre in Portugal were included. Demographic data and information on aetiology, smoking history, mMRC score, Bronchiectasis Severity Index (BSI) score, sputum characteristics, lung function, exacerbations, and radiological involvement degree were collected.

RESULTS

Patients included (mean age 54.7 ± 16.2 years; 60.8% females) were followed up for a period of 3.8 ± 1.7 years. The most common cause of bronchiectasis was infection (31.7%) followed by immune deficiencies (11.8%), whereas in 29% of cases, no cause was identified. Haemophilus influenzae (32.3%) and Pseudomonas aeruginosa (30.1%) were the most common CBI-associated possible pathogenic microorganisms. CBI patients presented a higher follow-up time than no-CBI patients (p = 0.003), worse lung function, BSI (p < 0.001), and radiological (p < 0.001) scores, and more prominent daily sputum production (p = 0.002), estimated mean volume (p < 0.001), and purulent sputum (p < 0.001). The number of exacerbations/year (p = 0.001), including those requiring hospital admission (p = 0.009), were also higher in the CBI group. Independent CBI predictors were BSI score (OR 3.577, 95% CI 1.233⁻10.378), sputum characteristics (OR 3.306, 95% CI 1.107⁻9.874), and radiological score (OR 1.052, 95% CI 1.004⁻1.102).

CONCLUSION

According to the CBI status, two different sub-groups of patients were found on the basis of several clinical outcomes, emphasizing the importance of routine sputum microbiological monitoring. Further studies are needed to better characterize CBI profiles and to define the individual clinical impact of the most prevalent pathogenic microorganisms.

Diversity and association of HLA/KIR receptors with type 2 diabetes in South India

The present study was undertaken to delineate the association(s) of KIR-HLA combination in South Indian Type 2 diabetes mellitus (T2DM) patients. The T2DM patients (n = 343) and healthy controls (n = 309) were genotyped for KIR/HLA ligands by PCR-SSP method. The increased frequency of activatory KIR (aKIR) 2DS2 (OR = 1.91; p < 2.91 × 10^-4 ) was observed in patients suggesting a susceptible association. The frequencies of iKIR 2DL2 (OR = 0.38; p < 1.55 × 10^-5 ) and aKIRs 2DS1 (OR = 0.60; p < 0.001) and 3DS1 (OR = 0.52; p < 5.83 × 10^-5 ) were decreased in patients suggesting protective associations. The C1/C2 combinatorial analysis has revealed an increased frequency of C1⁺ /C2^- in T2DM patients (OR = 1.62; p < 0.014). The KIR "AB" genotype (OR = 2.41; p < 3.87 × 10^-5 ) was observed to be higher in patients. However, the "BB" genotype (OR = 0.32; p < 4.71 × 10^-7 ) was increased in controls. The KIR motifs, "Tel-B/B" (OR = 1.84; p < 0.007), were observed higher among patients. However, the frequency of "Tel-A/B" motif genotype was decreased in patients (OR = 0.56; p < 3.13 × 10^-4 ). The iKIR/HLA combinations such as 2DL2/3 +C1 and 3DL2+A3/A11 were increased in patients (OR = 3.90; p < 7.5 × 10^-5 ) suggesting susceptible associations. On the contrary, the aKIR+HLA combinations such as 2DS2+C1, 2DS1+C2 and 3DS1+Bw4 were less frequent in patients (OR = 0.32; p < 4.2 × 10^-4 ) suggesting protective associations. Thus, the present study clearly establishes the positive and negative associations of different KIR-HLA receptor combinations with T2DM in South India.

The Role of the Immune Response in the Pathogenesis of Bronchiectasis

Bronchiectasis is a prevalent respiratory condition characterised by permanent and abnormal dilation of the lung airways (bronchi). There are a large variety of causative factors that have been identified for bronchiectasis; all of these compromise the function of the immune response to fight infection. A triggering factor may lead to the establishment of chronic infection in the lower respiratory tract. The bacteria responsible for the lower respiratory tract infection are usually found as commensals in the upper respiratory tract microbiome. The consequent inflammatory response to infection is largely responsible for the pathology of this condition. Both innate and adaptive immune responses are activated. The literature has highlighted the central role of neutrophils in the pathogenesis of bronchiectasis. Proteases produced in the lung by the inflammatory response damage the airways and lead to the pathological dilation that is the pathognomonic feature of bronchiectasis. The small airways demonstrate infiltration with lymphoid follicles that may contribute to localised small airway obstruction. Despite aggressive treatment, most patients will have persistent disease. Manipulating the immune response in bronchiectasis may potentially have therapeutic potential.

Canonical and Cross-reactive Binding of NK Cell Inhibitory Receptors to HLA-C Allotypes Is Dictated by Peptides Bound to HLA-C

BACKGROUND

Human natural killer (NK) cell activity is regulated by a family of killer cell immunoglobulin-like receptors (KIRs) that bind human leukocyte antigen (HLA) class I. Combinations of KIR and HLA genotypes are associated with disease, including susceptibility to viral infection and disorders of pregnancy. KIR2DL1 binds HLA-C alleles of group C2 (Lys80). KIR2DL2 and KIR2DL3 bind HLA-C alleles of group C1 (Asn80). However, this model cannot explain HLA-C allelic effects in disease or the impact of HLA-bound peptides. The goal of this study was to determine the extent to which the endogenous HLA-C peptide repertoire can influence the specific binding of inhibitory KIR to HLA-C allotypes.

RESULTS

The impact of HLA-C bound peptide on inhibitory KIR binding was investigated taking advantage of the fact that HLA-C*05:01 (HLA-C group 2, C2) and HLA-C*08:02 (HLA-C group 1, C1) have identical sequences apart from the key KIR specificity determining epitope at residues 77 and 80. Endogenous peptides were eluted from HLA-C*05:01 and used to test the peptide dependence of KIR2DL1 and KIR2DL2/3 binding to HLA-C*05:01 and HLA-C*08:02 and subsequent impact on NK cell function. Specific binding of KIR2DL1 to the C2 allotype occurred with the majority of peptides tested. In contrast, KIR2DL2/3 binding to the C1 allotype occurred with only a subset of peptides. Cross-reactive binding of KIR2DL2/3 with the C2 allotype was restricted to even fewer peptides. Unexpectedly, two peptides promoted binding of the C2 allotype-specific KIR2DL1 to the C1 allotype. We showed that presentation of endogenous peptides or HIV Gag peptides by HLA-C can promote KIR cross-reactive binding.

CONCLUSION

KIR2DL2/3 binding to C1 is more peptide selective than that of KIR2DL1 binding to C2, providing an explanation for KIR2DL3-C1 interactions appearing weaker than KIR2DL1-C2. In addition, cross-reactive binding of KIR is characterized by even higher peptide selectivity. We demonstrate a hierarchy of functional peptide selectivity of KIR-HLA-C interactions with relevance to NK cell biology and human disease associations. This selective peptide sequence-driven binding of KIR provides a potential mechanism for pathogen as well as self-peptide to modulate NK cell activation through altering levels of inhibition.

Bronchiectasis: Current Concepts in Pathogenesis, Immunology, and Microbiology

Bronchiectasis is a disorder of persistent lung inflammation and recurrent infection, defined by a common pathological end point: irreversible bronchial dilatation arrived at through diverse etiologies. This suggests an interplay between immunogenetic susceptibility, immune dysregulation, bacterial infection, and lung damage. The damaged epithelium impairs mucus removal and facilitates bacterial infection with increased cough, sputum production, and airflow obstruction. Lung infection is caused by respiratory bacterial and fungal pathogens, including Pseudomonas aeruginosa, Haemophilus, Aspergillus fumigatus, and nontuberculous mycobacteria. Recent studies have highlighted the relationship between the lung microbiota and microbial-pathogen niches. Disease may result from environments favoring interleukin-17-driven neutrophilia. Bronchiectasis may present in autoimmune disease, as well as conditions of immune dysregulation, such as combined variable immune deficiency, transporter associated with antigen processing-deficiency syndrome, and hyperimmunoglobulin E syndrome. Differences in prevalence across geography and ethnicity implicate an etiological mix of genetics and environment underpinning susceptibility.

Chronic Infection by Mucoid Pseudomonas aeruginosa Associated with Dysregulation in T-Cell Immunity to Outer Membrane Porin F

RATIONALE

Pseudomonas aeruginosa (PA) is an environmental pathogen that commonly infects individuals with cystic fibrosis (CF) and non-CF bronchiectasis, impacting morbidity and mortality. To understand the pathobiology of interactions between the bacterium and host adaptive immunity and to inform rational vaccine design, it is important to understand the adaptive immune correlates of disease.

OBJECTIVES

To characterize T-cell immunity to the PA antigen outer membrane porin F (OprF) by analyzing immunodominant epitopes in relation to infection status.

METHODS

Patients with non-CF bronchiectasis were stratified by frequency of PA isolation. T-cell IFN-γ immunity to OprF and its immunodominant epitopes was characterized. Patterns of human leukocyte antigen (HLA) restriction of immunodominant epitopes were defined using HLA class II transgenic mice. Immunity was characterized with respect to cytokine and chemokine secretion, antibody response, and T-cell activation transcripts.

MEASUREMENTS AND MAIN RESULTS

Patients were stratified according to whether PA was never, sometimes (<50%), or frequently (≥50%) isolated from sputum. Patients with frequent PA sputum-positive isolates were more likely to be infected by mucoid PA, and they showed a narrow T-cell epitope response and a relative reduction in Th1 polarizing transcription factors but enhanced immunity with respect to antibody production, innate cytokines, and chemokines.

CONCLUSIONS

We have defined the immunodominant, HLA-restricted T-cell epitopes of OprF. Our observation that chronic infection is associated with a response of narrowed specificity, despite strong innate and antibody immunity, may help to explain susceptibility in these individuals and pave the way for better vaccine design to achieve protective immunity.

Genome-wide association study for levels of total serum IgE identifies HLA-C in a Japanese population

Most of the previously reported loci for total immunoglobulin E (IgE) levels are related to Th2 cell-dependent pathways. We undertook a genome-wide association study (GWAS) to identify genetic loci responsible for IgE regulation. A total of 479,940 single nucleotide polymorphisms (SNPs) were tested for association with total serum IgE levels in 1180 Japanese adults. Fine-mapping with SNP imputation demonstrated 6 candidate regions: the PYHIN1/IFI16, MHC classes I and II, LEMD2, GRAMD1B, and chr13∶60576338 regions. Replication of these candidate loci in each region was assessed in 2 independent Japanese cohorts (n = 1110 and 1364, respectively). SNP rs3130941 in the HLA-C region was consistently associated with total IgE levels in 3 independent populations, and the meta-analysis yielded genome-wide significance (P = 1.07×10⁻¹⁰). Using our GWAS results, we also assessed the reproducibility of previously reported gene associations with total IgE levels. Nine of 32 candidate genes identified by a literature search were associated with total IgE levels after correction for multiple testing. Our findings demonstrate that SNPs in the HLA-C region are strongly associated with total serum IgE levels in the Japanese population and that some of the previously reported genetic associations are replicated across ethnic groups.

Distribution of Killer cell immunoglobulin like receptor genes in end stage renal disease among North Indian population

INTRODUCTION

NK cell function is regulated by cell surface inhibitory and activating receptors including the C-type lectin receptors and Killer Immunoglobulin-like receptors (KIR). The effect of immune modulating cytokines produced by NK cells in the pathogenesis of end stage renal disease (ESRD) remained intriguing. In this regard the present study assesses the combinatorial association of KIR gene content and KIR receptor-HLA ligand in the North Indian ESRD patients.

MATERIAL AND METHODS

KIR gene polymorphism as a susceptible marker in ESRD among 512 patients and 512 ethnically matched controls was analyzed. PCR-SSP based genotyping for KIR gene content and HLA-A, B, C typing was carried out.

RESULTS

Significant difference in frequencies of KIR2DS1-HLA-C2 (p≤0.0001, OR=1.98, CI=1.50-2.61), KIR2DS2-HLAC1 (p≤0.0001, OR=1.87, CI=1.42-2.46), KIR3DS1-HLA-Bw4 (p=0.0038, OR=1.46, CI=1.13-1.88) combinations for ESRD was found. In the combinatorial analysis Bw4(+)/3DL1(-)/3DS1(+) (p≤0.0001, OR=4.90, CI=2.75-8.71) and C1(+)/2DL2(-)/2DL3(-)/2DS2(+)/2DS3(+) (p=0.0037, OR=2.50, CI=1.35-4.63) showed risk association. KIR3DS1 was observed to be susceptible for all four primary kidney disease groups.

CONCLUSION

NK cell de-regulation due to HLA ligand binding KIR receptors may be involved in the patho-physiology of ESRD. Upon analyzing the data in this context it was found that C2/C2 donor might improve the clinical outcome of patients having C2 ligands.

Immune mechanisms and the impact of the disrupted lung microbiome in chronic bacterial lung infection and bronchiectasis

Recent studies analysing immunogenetics and immune mechanisms controlling susceptibility to chronic bacterial infection in bronchiectasis implicate dysregulated immunity in conjunction with chronic bacterial infection. Bronchiectasis is a structural pathological end-point with many causes and disease associations. In about half of cases it is termed idiopathic, because it is of unknown aetiology. Bronchiectasis is proposed to result from a 'vicious cycle' of chronic bacterial infection and dysregulated inflammation. Paradoxically, both immune deficiency and excess immunity, either in the form of autoimmunity or excessive inflammatory activation, can predispose to disease. It appears to be a part of the spectrum of inflammatory, autoimmune and atopic conditions that have increased in prevalence through the 20th century, attributed variously to the hygiene hypothesis or the 'missing microbiota'. Immunogenetic studies showing a strong association with human leucocyte antigen (HLA)-Cw*03 and HLA-C group 1 homozygosity and combinational analysis of HLA-C and killer immunoglobulin-like receptors (KIR) genes suggests a shift towards activation of natural killer (NK) cells leading to lung damage. The association with HLA-DR1, DQ5 implicates a role for CD4 T cells, possibly operating through influence on susceptibility to specific pathogens. We hypothesize that disruption of the lung microbial ecosystem, by infection, inflammation and/or antibiotic therapy, creates a disturbed, simplified, microbial community ('disrupted microbiota') with downstream consequences for immune function. These events, acting with excessive NK cell activation, create a highly inflammatory lung environment that, in turn, permits the further establishment and maintenance of chronic infection dominated by microbial pathogens. This review discusses the implication of these concepts for the development of therapeutic interventions.

The overlap of bronchiectasis and immunodeficiency with asthma

Bronchiectasis should be considered as a differential diagnosis for, as well as a comorbidity in, patients with asthma, especially severe or long-standing asthma. Chronic airway inflammation is thought to be the primary cause, as with chronic or recurrent pulmonary infection and autoimmune conditions that involve the airways. Consequently, immunodeficiencies with associated increased susceptibility to respiratory tract infections or chronic inflammatory airways also increase the risk of developing bronchiectasis. Chronic bronchiectasis is associated with impaired mucociliary clearance and increased bronchial secretions, leading to airway obstruction and airflow limitation, which can lead to exacerbation of underlying asthma or increased asthma symptoms.

Trends in bronchiectasis among medicare beneficiaries in the United States, 2000 to 2007

BACKGROUND

Bronchiectasis is a potentially serious condition characterized by permanent and abnormal widening of the airways, the prevalence of which is not well described. We sought to describe the trends, associated conditions, and risk factors for bronchiectasis among adults aged ≥ 65 years.

METHODS

A 5% sample of the Medicare outpatient claims database was analyzed for bronchiectasis trends among beneficiaries aged ≥ 65 years from 2000 to 2007. Bronchiectasis was identified using International Classification of Diseases, Ninth Revision, Clinical Modification claim diagnosis codes for acquired bronchiectasis. Period prevalence was used to describe sex- and race/ethnicity-specific rates, and annual prevalence was used to describe trends and age-specific rates. We estimated trends using Poisson regression and odds of bronchiectasis using multivariate logistic regression.

RESULTS

From 2000 to 2007, 22,296 people had at least one claim for bronchiectasis. The 8-year period prevalence of bronchiectasis was 1,106 cases per 100,000 people. Bronchiectasis increased by 8.7% per year. We identified an interaction between the number of thoracic CT scans and race/ethnicity; period prevalence varied by a greater degree by number of thoracic CT scans among Asians compared with whites or blacks. Among people with one CT scan, Asians had a 2.5- and 3.9-fold higher period prevalence compared with whites and blacks.

CONCLUSIONS

Bronchiectasis prevalence increased significantly from 2000 to 2007 in the Medicare outpatient setting and varied by age, sex, and race/ethnicity. This increase could be due to a true increase in the condition or an increased recognition of previously undiagnosed cases.

Mechanisms of immune dysfunction and bacterial persistence in non-cystic fibrosis bronchiectasis

Bronchiectasis is a chronic inflammatory lung disease. The underlying cause is not identified in the majority of patients, but bronchiectasis is associated with a number of severe infections, immunodeficiencies and autoimmune disorders. Regardless of the underlying cause, the disease is characterised by a vicious cycle of bacterial colonisation, airway inflammation and airway structural damage. Inflammation in bronchiectasis is predominantly neutrophil driven. Neutrophils migrate to the airway under the action of pro-inflammatory cytokines such as interleukin-8, tumour necrosis factor-α and interleukin-1β, all of which are increased in the airway of patients with bronchiectasis. Bacterial infection persists in the airway despite large numbers of neutrophils that would be expected to phagocytose and kill pathogens under normal circumstances. Evidence suggests that neutrophils are disabled by multiple mechanisms including cleavage of phagocytic receptors by neutrophil elastase and inhibition of phagocytosis by neutrophil peptides. Complement activation is impaired and neutrophil elastase may cleave activated complement from pathogens preventing effective opsonisation. Organisms also evade clearance by adapting to chronic infection. The formation of biofilms, reduced motility and the down-regulation of virulence factors are among the strategies used to subvert innate immune mechanisms. Greater understanding of the mechanisms underlying chronic colonisation in bronchiectasis will assist in the development of new treatments for this important disease.

The immune response and its therapeutic modulation in bronchiectasis

Bronchiectasis (BC) is a chronic pulmonary disease with tremendous morbidity and significant mortality. As pathogen infection has been advocated as a triggering insult in the development of BC, a central role for the immune response in this process seems obvious. Inflammatory cells are present in both the airways as well as the lung parenchyma, and multiple mediators of immune cells including proteases and cytokines or their humoral products are increased locally or in the periphery. Interestingly, a defect in the immune system or suppression of immune response during conditions such as immunodeficiency may well predispose one to the devastating effects of BC. Thus, the outcome of an active immune response as detrimental or protective in the pathogenesis of BC may be dependent on the state of the patient's immunity, the severity of infection, and the magnitude of immune response. Here we reassess the function of the innate and acquired immunity in BC, the major sites of immune response, and the nature of the bioactive mediators. Furthermore, the potential link(s) between an ongoing immune response and structural alterations accompanying the disease and the success of therapies that can modulate the nature and extent of immune response in BC are elaborated upon.

Association of KIR genotypes and haplotypes with syphilis in a Chinese Han population

Killer immunoglobulin-like receptors (KIRs) can regulate the activation of NK and T cells in response to infection. Syphilis is a sexually transmitted infection caused by the Treponema pallidum subspecies pallidum spirochete bacterium. The objective of this study was to explore whether KIR genotypes and haplotypes were associated with syphilis in a Chinese Han population. Polymerase chain reaction with sequence-specific primers (PCR-SSP) was used to identify the KIR genotypes in 190 patients with syphilis and 192 healthy controls. The frequency of genotype P was higher in healthy controls than that in patients with syphilis (P = 0.002), and its OR was 0.304, while the frequencies of genotypes AE and AG were higher in patients with syphilis than those in healthy controls. The frequency of haplotype 17 was lower, and its OR was 0.321, whereas the frequencies of haplotype 1 and 6 were higher in patients with syphilis than those in healthy controls. KIR haplotypes A and B have distinctive centromeric (Cen) and telomeric (Tel) gene content motifs. The frequency of Tel-B/B was higher in patients with syphilis than that in healthy controls (P = 0.024). Based on these findings, it seems that individuals with the genotype AE, AG or Tel-B/B, or haplotypes 1 and 6 are susceptible to syphilis, whereas individuals with genotype P or haplotype 17 are protective from syphilis in the Chinese Han population.

Human leukocyte antigen-C and killer cell immunoglobulin-like receptor gene polymorphisms among patients with syphilis in a Chinese Han population

Syphilis is a sexually transmitted infection caused by the Treponema pallidum subspecies pallidum spirochete bacterium. The killer cell immunoglobulin-like receptors (KIR), interacting with human leukocyte antigens (HLA), regulate the activations of natural killer (NK) cells and certain T-cell subsets in response to microbe infection. The objective of this study was to explore whether KIR and HLA-C gene polymorphisms were associated with syphilis in a Chinese Han population. Polymerase chain reaction with sequence-specific primers (PCR-SSP) method was used to genotype KIR and HLA-C genes in 231 syphilis patients and 247 healthy controls. Framework genes KIR2DL4, KIR3DL2, KIR3DL3 and KIR3DP1 were present in all individuals. The frequencies of KIR2DS3 and KIR3DS1 were higher in syphilis patients than in healthy controls (p = 0.030 and p = 0.038, respectively), while the frequency of KIR2DS5 was higher in healthy controls than in syphilis patients (p = 0.015; OR = 0.575). The homozygote for HLA-C1 allele (HLA-C1C1) was more common in controls compared with syphilis patients (p = 0.030; OR = 0.667). The frequency of individuals with HLA-C1C1 and KIR2DL3 genotype was higher in control group relative to syphilis patient group (p = 0.018; OR = 0.647). These data indicated that KIR2DS3 and KIR3DS1 were more prevalent in syphilis patients than in controls, and that KIR2DS5, HLA-C1C1 and HLA-C1C1-KIR2DL3 were more prevalent in controls than in syphilis patients, respectively. These will require further investigation using functional studies.

Association of killer cell immunoglobulin-like receptor and human leukocyte antigen-C genotype with dry eye disease in a Chinese Han population

Dry eye is one of the most prevalent eye diseases and dry eye disease (DED) is associated with ocular surface inflammation. The interaction between killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigens (HLAs) regulates the activation of natural killer (NK) cells and certain T cell subsets in response to inflammation. The objective of this study was to explore whether KIR gene and HLA-C allele polymorphisms were associated with DED in a Chinese Han population. Polymerase chain reaction with sequence-specific primers method was used to genotype KIR genes and HLA-C alleles in 106 DED patients and 220 healthy controls. Framework genes KIR2DL4, KIR3DL2, KIR3DL3, and KIR3DP1 were present in all individuals. There were no significant differences in the frequencies of inhibitory KIR genes between the two groups. However, the frequency of KIR2DS2 was significantly higher in severe DED patients than that in healthy controls (p=0.031, odds ratio [OR]=1.828, 95% confidence interval [CI]=1.05-3.17). Significantly different distributions of HLA-C allele groups were not observed in severe DED patients and controls. The frequency of the combination of HLA-C1 allele group with KIR2DS2 was significantly higher in severe DED patients compared with controls (p=0.013, OR=2.083, 95% CI=1.16-3.74). These data suggested that this genotype combination was associated with susceptibility to severe DED and that NK cells might have a role in the pathogenesis of DED. The results led to an interesting future research question of whether or not KIR and HLA-C genotypes were involved in the predisposition to or pathogenesis of DED.

KIR-HLA genotypes in HIV-infected patients lacking immunological recovery despite effective antiretroviral therapy

Background

In HIV-infected individuals, mechanisms underlying unsatisfactory immune recovery during effective combination antiretroviral therapy (cART) have yet to be fully understood. We investigated whether polymorphism of genes encoding immune-regulating molecules, such as killer immunoglobulin-like receptors (KIR) and their ligands class I human leukocyte antigen (HLA), could influence immunological response to cART.

Methods

KIR and HLA frequencies were analyzed in 154 HIV-infected and cART-treated patients with undetectable viral load divided into two groups: ‘immunological non responders’ (INR, N = 50, CD4⁺ T-cell count <200/mm³) and full responders (FR, N = 104, CD4⁺ T-cell count >350/mm³). Molecular KIR were typed using polymerase chain reaction-based genotyping. Comparisons were adjusted for baseline patient characteristics.

Results

The frequency of KIR2DL3 allele was significantly higher in FR than in INR (83.7% vs. 62%, P = 0.005). The functional compound genotype HLA-C1⁺/KIR2DL3⁺, even at multivariable analysis, when adjusted for nadir CD4⁺ T-cell count, was associated with reduced risk of INR status: odds ratio (95% Confidence Intervals) 0.34 (0.13−0.88), P = 0.03.

Conclusions

Reduced presence of the inhibitory KIR2DL3 genotype detected in INR might provoke an imbalance in NK function, possibly leading to increased immune activation, impaired killing of latently infected cells, and higher proviral burden. These factors would hinder full immune recovery during therapy.

Maternal KIR and fetal HLA-C: a fine balance

NK cell effector function is regulated by a range of activating and inhibitory receptors, and many of their known ligands are MHC class I molecules. Human NK receptors encoded by the Killer immunoglobulin-like receptor (KIR) gene family recognize polymorphic HLA-C as well as some HLA-A and HLA-B molecules. KIRs are expressed by uterine NK (uNK) cells, which are distinctive NK cells directly in contact with the invading fetal placental cells that transform the uterine arteries during the first trimester. Trophoblast cells express both maternal and paternal HLA-C allotypes and can therefore potentially interact with KIRs expressed by uNK. Therefore, allorecognition of paternal HLA-C by maternal KIR might influence trophoblast invasion and vascular remodeling, with subsequent effects on placental development and the outcome of pregnancy. We discuss here the studies relating to KIR/HLA-C interactions with an emphasis on how these function during pregnancy to regulate placentation.

Killer immunoglobulin-like receptor and human leukocyte antigen-C genotypes in rheumatoid arthritis primary responders and non-responders to anti-TNF-α therapy

The identification of patients who will respond to anti-tumor necrosis factor alpha (anti-TNF-α) therapy will improve the efficacy, safety, and economic impact of these agents. We investigated whether killer cell immunoglobulin-like receptor (KIR) genes are related to response to anti-TNF-α therapy in patients with rheumatoid arthritis (RA). Sixty-four RA patients and 100 healthy controls were genotyped for 16 KIR genes and human leukocyte antigen-C (HLA-C) group 1/2 using polymerase chain reaction sequence-specific oligonucleotide probes (PCR-SSOP). Each patient received anti-TNF-α therapy (adalimumab, etanercept, or infliximab), and clinical responses were evaluated after 3 months using the disease activity score in 28 joints (DAS28). We investigated the correlations between the carriership of KIR genes, HLA-C group 1/2 genes, and clinical data with response to therapy. Patients responding to therapy showed a significantly higher frequency of KIR2DS2/KIR2DL2 (67.7% R vs. 33.3% NR; P = 0.012). A positive clinical outcome was associated with an activating KIR-HLA genotype; KIR2DS2 (+) HLA-C group 1/2 homozygous. Inversely, non-response was associated with the relatively inhibitory KIR2DS2 (-) HLA-C group 1/2 heterozygous genotype. The KIR and HLA-C genotype of an RA patient may provide predictive information for response to anti-TNF-α therapy.

Killer immunoglobulin-like receptors (KIRs) and HLA-C allorecognition patterns implicative of dominant activation of natural killer cells contribute to recurrent miscarriages

BACKGROUND

Decidual natural killer (NK) cells play key developmental roles at the feto-maternal interface. Individual differences in NK-cell interactions are dependent on the combinations of variable killer immunoglobulin-like receptor (KIR) and HLA class-I gene products. As different receptor-ligand interactions may result in altered NK-cell-mediated immunity against pathogens, it is proposed that the relationship between these genes may be important in a state such as recurrent miscarriage (RM). We had earlier reported that the predisposition to RM is influenced by the maternal KIR gene content. In the present study, we have attempted to extend our findings in the light of contribution from the paternal antigens on the outcome of pregnancy, since maternal NK cells may potentially encounter non-self-paternal HLA-C alleles on trophoblasts. All HLA-C allotypes fall into two major KIR epitopes--C1 (HLA-C*01/*03/*07/*08/*12/*14/*16) and C2 (HLA-C*02/*04/*05/*06/*15/*17/*18)--on the basis of a dimorphism at position 80 of the α1 domain.

METHODS

PCR-sequence specific primer-based genotyping was used to determine the maternal KIR gene content and HLA-C genotypes down to allele level in couples experiencing RM and controls.

RESULTS

KIR2DL1 with both partners homozygous for HLA C2 was significantly higher in control couples when compared with the patients [P = 0.0004, odds ratio (OR) = 0.28, 95% confidence interval (CI) = 0.13-0.58]. The activating KIR2DS2 with both partners homozygous for HLA C1 was significantly higher in patients when compared with the controls (P = 0.002, OR = 2.83, 95% CI = 1.47-5.40).

CONCLUSIONS

Our results represented the 'top-end' of the activation spectrum of KIR-HLA-C compound genotype for NK cells and this may contribute to the immunological etiology of RM.

Inhibitory KIR and specific HLA-C gene combinations confer susceptibility to or protection against chronic hepatitis B

Antiviral activity of natural killer (NK) cells is regulated partially through inhibitory and activating killer cell immunoglobulin-like receptors (KIR) interacting with human leukocyte antigen C (HLA-C) ligands. The highly polymorphic nature of HLA-C and KIR genes endows individuals with diverse HLA-C/KIR combinations, which may confer susceptibility to or protection against a certain challenge. We analyzed the genes encoding KIR receptors and HLA-C ligands and HLA-C/KIR combinations in patients with chronic hepatitis B and healthy subjects. We found that inhibitory receptor KIR2DL1 in combination with HLA-C2 ligand confers susceptibility to chronic hepatitis B (CHB), whereas inhibitory receptor KIR2DL3 or KIR2DL3 homozygote in the presence of HLA-C1C1 genotype shows protection against CHB. Our data reveal that inhibitory NK cell interactions are important in determining antiviral immunity and that distinct affinity inhibitory responses will exert different impact on the development of CHB.

Killer Ig-like receptor (KIR) genotype predicts the capacity of human KIR-positive CD56dim NK cells to respond to pathogen-associated signals

IFN-gamma emanating from NK cells is an important component of innate defense against infection. In this study, we demonstrate that, following in vitro stimulation of human peripheral blood NK cells with a variety of microbial ligands, CD56(dim) as well as CD56(bright) NK cells contribute to the overall NK cell IFN-gamma response with, for most cell donors, IFN-gamma(+) CD56(dim) NK cells outnumbering IFN-gamma(+) CD56(bright) NK cells. We also observe that the magnitude of the human NK IFN-gamma response to microbial ligands varies between individuals; that the antimicrobial response of CD56(bright), but not CD56(dim), NK cells is highly correlated with that of myeloid accessory cells; and that the ratio of IFN-gamma(+) CD56(dim) to IFN-gamma(+) CD56(bright) NK cells following microbial stimulation differs between individuals but remains constant for a given donor over time. Furthermore, ratios of IFN-gamma(+) CD56(dim) to IFN-gamma(+) CD56(bright) NK cells for different microbial stimuli are highly correlated and the relative response of CD56(dim) and CD56(bright) NK cells is highly significantly associated with killer Ig-like receptor (KIR) genotype. These data reveal an influence of KIR genotype, possibly mediated via NK cell education, on the ability of NK cells to respond to nonviral infections and have implications for genetic regulation of susceptibility to infection in humans.

The Yin and Yang of HLA and KIR in human disease

Killer cell immunoglobulin-like receptors (KIR) are expressed on natural killer (NK) cells and subsets of T cells. The KIR genes are polymorphic and the KIR gene complex is polygenic with varying numbers of inhibitory and activating receptors. HLA class I molecules serve as ligands for the KIR. Interactions of the independently segregating KIR and HLA loci are important for recognition of targets by NK cells as well as NK cell 'licensing'. Several disease association studies indicate a role for interactions between these loci in infectious diseases, autoimmune/inflammatory disorders, cancer and reproduction. Emerging functional data supports a mechanism based on a continuum of inhibition to activation through various compound KIR-HLA genotypes in diseases.

A study of the killer cell immunoglobulin-like receptor gene KIR2DS1 in a Caucasoid Brazilian population with psoriasis vulgaris

Psoriasis is a chronic inflammatory skin disease whose pathogenesis and genetic background remain unclear. Considering that previous studies have suggested an association of psoriasis vulgaris (PV) and killer cell immunoglobulin-like receptors (KIRs), we typed 15 KIR genes and human leukocyte antigen (HLA)-Cw in 79 Brazilian Caucasoid patients with PV and 110 healthy controls by polymerase chain reaction (PCR) using sequence-specific oligonucleotides and sequence-specific primers. We did not observe a relevant increase in the frequency of the activating KIR2DS1 gene in the PV group [KIR2DS1, 46 of 79 cases (58.2%) vs 40 of 110 controls (36.4%)]. However, an association of KIR2DS1 with Cw*0602+ in 26.5% of PV patients was observed, while it was present in only 5.4% of controls. These results suggest that activating KIR2DS1 gene may not confer susceptibility to PV, and an association of KIR2DS1 gene with the HLA-Cw*0602+ was observed in these patients.

Regulation of immunity in bronchiectasis

Bronchiectasis is a chronic, progressive lung disease where there is irreversible, abnormal dilatation of one or more bronchi, with chronic airway inflammation, associated chronic cough and sputum production, recurrent chest infections, and airflow obstruction. As such it is essentially a pathological endpoint with several underlying causes. Allergic bronchopulmonary aspergillosis (ABPA) is an important cause of bronchiectasis and aspergillus related lung disease sometimes complicates established bronchiectasis. A diagnosis of bronchiectasis is made clinically and confirmed with high-resolution computed tomography (HRCT) of the thorax. Progressive lung damage results from a 'vicious cycle' of recurrent bacterial infection and a poorly regulated inflammatory response. There appear to be two stages to the disease process: the initial insult that sets off the disease and then the ongoing, inflammatory process encompassing recurrent infection and progressive lung damage. Abnormalities in innate and adaptive immunity may predispose to bronchiectasis at both stages. Recent immunogenetic evidence suggests that there may be a link between the level of natural killer (NK) cell activation and disease susceptibility, implicating a predisposing role for innate immune mechanisms. A role for adaptive immune mechanisms is suggested by the genetic association of HLA-DR1, DQ5 with increased susceptibility to idiopathic bronchiectasis.

Age-related macular degeneration is associated with the HLA-Cw*0701 Genotype and the natural killer cell receptor AA haplotype

PURPOSE

To determine the association of human leukocyte antigen (HLA) C and its cognate killer cell immunoglobulin-like receptor (KIR) ligands with age-related macular degeneration (AMD).

METHODS

HLA class I allele groups including the HLA-C principal alleles were genotyped in a cohort of 104 AMD cases and 93 controls by using the PCR-SSP (sequence-specific primers)

METHOD

This cohort was then genotyped for 16 KIR genes by PCR-SSP. Frequencies of the tested HLA/KIR alleles were then compared between patients with AMD and normal control subjects. HLA-C1, -Cw*07, and -Cw*0701 genotypes and their combinations with KIR genotypes/haplotypes were tested for association with AMD. Probabilities were obtained with a two-tailed chi(2) test and Bonferroni correction applied for multiple testing (P(c)).

RESULTS

The HLA-Cw*0701 allele, in combination with the inhibitory KIR AA haplotype was associated with AMD after logistic regression analysis (P = 0.006, P(c) = 0.036, OR = 4.35, 95% CI = 1.41-13.44).

CONCLUSIONS

The HLA-Cw*0701 allele and KIR haplotype AA are associated with AMD. This genotype combination suggests that natural killer cells have a role in the pathogenesis of AMD. Replication studies are needed to confirm these novel HLA-KIR associations with AMD.

Polymorphisms of KIRs gene and HLA-C alleles in patients with ankylosing spondylitis: possible association with susceptibility to the disease

INTRODUCTION

An emerging body of evidence is accumulating to suggest that killer cell immunoglobulin-like receptors (KIRs) and human leukocyte antigen (HLA) class I ligands contribute to the pathogenesis of diverse kinds of autoimmune diseases. However, the functional effects of their polymorphism remain largely unknown to date. Thus, the present study was undertaken to determine the association of the polymorphisms KIRs gene and HLA-C alleles with the susceptibility to ankylosing spondylitis (AS) by means of polymerase chain reaction/sequence-specific primers for genotyping KIRs from genomic DNA of 119 patients with AS together with 128 healthy donors as a control group.

RESULTS AND DISCUSSION

We found that the frequencies of KIR3DS1 and KIR2DL5 were statistically significantly higher in the patient group than those in the control group (P = 0.016 and P = 0.003, respectively). Meanwhile, the percentage of patients, who were carrying two or more of the activating KIRs, was higher than that of control group. With respect to HLA-C alleles, individuals with AS showed an increased frequency of HLA-Cw02. If HLA-C was divided into group 1 or group 2 based on whether there was an asparagine or lysine present at position 80 of the alpha-chain, HLA-C group 2 was more common in subjects with AS compared to control subjects. The genotype 2DS1+/HLA-C lys(80)+ was more common in subjects with AS. Moreover, the CD69 expression, a NK activation marker, remarkably increased in patient with AS.

CONCLUSION

In conclusions, this study suggests that KIR3DS1 may severe as AS susceptive genes to trigger continuous injury of arthrosis. The imbalance of activating and inhibitory KIR as well as HLA-C group 1 and group 2 may be the key factor, which influences the pathogenesis of AS. Moreover, KIR2DS1 might associate with the susceptibility of AS by influencing NK cell activity once group 2 HLA-C ligands are present.

Human leucocyte antigen class II association in idiopathic bronchiectasis, a disease of chronic lung infection, implicates a role for adaptive immunity

The aetiology of idiopathic bronchiectasis, a lung disease where chronic inflammation and bacterial infection leads to progressive lung damage, is unknown. A possible role for natural killer cells has been highlighted previously. However, a role for adaptive immunity is suggested by the presence of CD4 and CD8 T cells in diseased lung tissue. Evidence of a human leucocyte antigen (HLA) class II disease association would further implicate a role for adaptive immunity. To establish if there is any HLA association, we analysed HLA-A, HLA-B, HLA-DQA1, HLA-DQB1 and HLA-DRB1 alleles in patients with idiopathic bronchiectasis and controls. Genomic DNA from 92 adults with idiopathic bronchiectasis and 101 healthy controls was analysed by polymerase chain reaction with sequence-specific primers. We found an increase in the prevalence of HLA-DRB1*01 DQA1*01/DQB1*05 genes in idiopathic bronchiectasis; that is, the HLA-DR1, DQ5 haplotype (odds ratio 2.19, 95% confidence interval 1.15-4.16, P = 0.0152) compared with control subjects. The association with HLA-DR1, DQ5 implicates a role for CD4 T cells restricted by these molecules in susceptibility to the progressive lung damage seen in this disease. This may operate either through influencing susceptibility to specific pathogens or to self-reactivity and requires further investigation.

Natural killer cells, killer immunoglobulin-like receptors and human leucocyte antigen class I in disease

Natural killer cells constitute a potent, rapid part of the innate immune response to infection or transformation, and also generate a link to priming of adaptive immunity. Their function can encompass direct cytotoxicity as well as the release of cytokines and chemokines. In humans, a major component of natural killer (NK) cell target recognition depends mainly on the surveillance of human leucocyte antigen (HLA) class I molecules by killer immunoglobulin-like receptors (KIR). Different KIR can transmit inhibitory or activatory signals to the cell, and effector function is considered to result from the balance of these contributing signals. The regulation of NK cell responses depends on a number of variables: KIR genotype, HLA genotype, heterozygosity versus homozygosity for these, whether there is cognate recognition between the HLA and KIR products carried by an individual, clonal variation between individual NK cells in KIR expression, and the specific modulation of HLA expression by infection, transformation or peptide binding. Different HLA/KIR genotypes can impart different thresholds of activation to the NK cell repertoire and such genotypic variation has been found to confer altered risk in a number of diseases including human immunodeficiency virus (HIV) susceptibility and progression, hepatitis C virus clearance, idiopathic bronchiectasis, autoimmunity and cancer.

KIR and disease: a model system or system of models?

The discovery of an unexpected level of diversity among the killer cell immunoglobulin-like receptors has led to a search for their role in human disease. Due to their polymorphism and also that of their human leukocyte antigen class I ligands, these studies are difficult to perform and complex to interpret. Nevertheless, as the number of data sets increase, consistent trends and themes are beginning to emerge in both viral and inflammatory disorders. In this review, we summarize the findings from a number of disease association studies and discuss these in the context of the activating and inhibitory roles of the members of this gene family.

Aetiology in adult patients with bronchiectasis

BACKGROUND

Bronchiectasis has a number of causes. Their prevalence is not well documented. The aim of this study was to identify aetiology in a population of patients referred to a specialist clinic with symptoms suggestive of bronchiectasis, to determine the proportion of patients in whom knowing the aetiology altered management. In addition we wished to describe in detail those patients who remained idiopathic to facilitate future studies of this group; and establish the diagnosis in those without bronchiectasis.

METHODS

A total of 240 consecutive patients referred to the Royal Brompton Hospital with a history of recurrent chest infections, chronic cough and regular sputum production underwent a 3 day program of investigation.

RESULTS

A total of 165 patients had bronchiectasis on CT scan, an underlying cause was identified in 122 (74%) and this affected management in 61 (37%). The common aetiologies were: post-infection (52), primary ciliary dyskinesia (17), allergic bronchopulmonary aspergillosis (13), and immune deficiency (11). Fourty-three patients had idiopathic bronchiectasis. They had symmetrical predominant lower lobe disease with onset of chronic chest and sinus symptoms in middle age.

CONCLUSION

Full investigation of problematic cases should occur in a specialist centre because results affect management in a third of cases.

IFN? and CXCR-1 gene polymorphisms in idiopathic bronchiectasis

Idiopathic bronchiectasis is a disease of chronic, bacterial lung infection, unresolving inflammation and progressive lung damage. Bronchiectasis can be associated with autoimmune diseases including ulcerative colitis. Defects of both innate and adaptive immunity have been proposed. The airway inflammation is characterized by interleukin-8 (IL-8) expression and infiltration by neutrophils and T cells. Here we investigated two candidate gene polymorphisms that may contribute to disease susceptibility: a CXCR-1 (+2607 G/C) gene polymorphism that is implicated in IL-8 binding and neutrophil trafficking as well as the interferon-gamma (IFNgamma) (+874 T/A) polymorphism which is linked to levels of IFNgamma production. These polymorphisms were distributed similarly in the idiopathic bronchiectasis group and controls, suggesting that these two candidate gene polymorphisms are not associated with disease susceptibility.

HLA-C expression pattern is spatially different between psoriasis and eczema skin lesions

Interactions between genetic and environmental factors underlie the immune dysregulation and keratinocyte abnormalities that characterize psoriasis. Among known psoriasis susceptibility loci (PSORS), PSORS1 on chromosome 6 has the strongest association to disease. Altered expression of some PSORS1 candidate genes has been reported but little is known about HLA-C expression in psoriasis. This study compared expression of major histocompatibility complex class Ia and HLA-C in psoriasis, allergic contact eczema, and normal skin. Although HLA-C was abundant in protein extracts from both eczema and psoriasis, a consistent and intriguing difference in the expression pattern was observed; strong immunoreactivity in the basal cell layer, polarized towards the basement membrane in psoriasis, whereas in eczema lesions HLA-C immunostaining was present mostly in suprabasal cells. Inflammatory cells in the dermis were strongly stained in both diseases. Normal skin epithelium showed less intense but similar HLA-C staining as eczema lesions. HLA class Ia expression overall resembled that of HLA-C in all samples. The distinct HLA-C expression patterns in psoriasis and eczema suggest a functional role in the specific psoriasis immune response and not only a general feature of inflammation.

The killer immunoglobulin-like receptor gene cluster: tuning the genome for defense

Killer immunoglobulin-like receptors (KIRs) are molecules expressed on the surface of natural killer (NK) cells, which play an important role in innate immunity. KIR recognition of major histocompatability complex (MHC) class I allotypes represents one component of the complex interactions between NK cells and their targets in determining NK cell reactivity. KIRs are encoded by a gene cluster at human chromosome 19q13.4. Despite their high degree of sequence identity, KIR genes encode proteins that have diverse recognition patterns (specific HLA class I allotypes) and confer opposing signals (activating or inhibitory) to the NK cell. The KIR gene cluster is highly polymorphic, with individual genes exhibiting allelic variability and individual haplotypes differing in gene content. The polymorphism of the KIR locus parallels that of the MHC, facilitating the adaptation of the immune system to a dynamic, challenging environment. This variation is associated with a growing number of human diseases, which is likely to extend to levels observed for the HLA loci. Here we review current progress in understanding KIR biology and genetics.