Experimental Gerontology 39 (2004) 1223-1232 www.elsevier.com/locate/expgero

Genetic Diversity of KIR in Immunosenescence and Longevity within the Irish Population

D. Maxwell a,b,*, Owen A. Ross a,b, Martin D. Curran b, I. Maeve Rea c, Derek Middleton a,d

a School of Biology and Biochemistry, Queen's University of Belfast, 97 Lisburn Road, Northern Ireland
b Department of Geriatric Medicine, Queen's University of Belfast, Northern Ireland, UK
c School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, UK
d Northern Ireland Regional Histocompatibility and Immunogenetics Laboratory, Blood Transfusion Building, City Hospital, Belfast BT9 7TS, Northern Ireland, UK

Received 23 March 2004; received in revised form 19 May 2004; accepted 26 May 2004
Available online 19 June 2004

Abstract

Natural killer (NK) cells play a pivotal role in the innate immune response. During the ageing process, variations occur in NK cell number and function. The cytolytic activity of NK cells is controlled by an array of activating and inhibitory cell surface receptors, including the killer cell immunoglobulin-like receptors (KIRs). In the present study, genetic diversity of the KIR loci was analyzed with respect to successful ageing in the Irish population. A PCR-SSOP KIR gene identification system was employed to determine the frequency of the named KIR genes/pseudogenes and KIR genotypes within a healthy aged cohort and young control group. Although two KIR genes (2DS3, 2DL5) displayed an initial increased frequency in the aged group, this association lost significance when repeated in a second cohort. Given the lack of studies to date investigating the role of the KIR gene system in healthy ageing, further analysis of KIR diversity is required to elucidate its role in age-related disease and longevity.

Keywords: Natural killer cell; KIR; Polymorphism; Ageing; Belfast

1. Introduction

Natural killer (NK) cells play a pivotal role in the innate immune response, and an increase in the number of NK cells is observed in healthy elderly individuals due to expansion of the functionally mature NK cell subset (McNerlan et al., 1998; Solana et al., 1999). Accompanying the rise in NK cell number, a decrease in cytotoxic capacity occurs on a per cell basis, and thus overall NK cell cytotoxicity in the healthy aged is maintained at a level comparable to young controls (Di Lorenzo et al., 1999; Miyaji et al., 2000). Studies suggesting that impaired NK cell activity is associated with atherosclerosis and death due to infection in the elderly have also been reported (Bruunsgaard et al., 2001; Ogata et al., 2001). These findings support the hypothesis that a well-preserved NK cell activity is important for successful aging.

Deterioration of the immune system with age (immunosenescence) and the associated increased susceptibility of the elderly to infectious disease, cancer, and autoimmune disorders have led to extensive investigation of immune parameters in the aged (Pawelec and Solana, 1997; Franceschi et al., 2000a; Malaguarnera et al., 2001). Several studies have reported a decline in T cell number and function and a decrease in B cell number, which collectively would result in impaired cellular and humoral immune responses (reviewed by Ginaldi et al., 1999). Accompanying the decline in adaptive immune function, alterations in certain cells that mediate non-specific immunity are also observed.

Due to their role in the innate response, NK cells provide a first line of defense against infectious agents and cancer (Malnati et al., 1993; Biron et al., 1999; Wu and Lanier, 2003) and are also thought to play a role in autoimmunity (Shi et al., 2000; Singal et al., 2000). NK cells mediate their immune function through the recognition and lysis of abnormal cells that either lack the expression or express inadequate amounts of human leukocyte antigen (HLA) class I molecules (Ljunggren and Karre, 1990). The ability of NK cells to discriminate between normal and HLA class I-deficient cells is due to the expression of clonally distributed HLA class I-specific inhibitory receptors (Radaev and Sun, 2003). Subsequent NK cell-mediated lysis of HLA class I-deficient cells arises from the expression of HLA class I-specific activating receptors by NK cell clonal populations (Biassoni etKIR genes represent two mechanisms underlying KIR polymorphism (Witt et al., 1999).

2.1. Subjects

One hundred unrelated control samples (59% female, 41% male with an age-range of 19-45 years old) were chosen at random from the DNA bank of anonymous healthy Caucasian individuals from the Northern Ireland population, stored at the Northern Ireland Histocompatibility and Immunogenetics Laboratory (NIHIL), Belfast City Hospital. Ninety-three unrelated aged samples (70% female, 30% male with an age-range of 80-97 years old) from the BELFAST study (Rea et al., 2000) were also included in the study. A second subset of 89 unrelated healthy control samples (69% female, 31% male with an age-range of 19-45 years) from the NIHIL DNA bank and 89 unrelated aged samples (70% female, 30% male with an age-range of 80-97 years) from the BELFAST study were analyzed in an attempt to confirm any significant findings following analysis of the first cohort of samples. All aged DNA samples were from healthy elderly Caucasian individuals from the BELFAST study of the Northern Ireland population displaying no signs of age-related disorders, still living independently and approximating SENIEUR status (Ligthart et al., 1984, 1990). Ethical approval was obtained from the Queens University of Belfast ethics committee.

2.2. KIR genotyping by PCR-SSOP