Experimental Gerontology 39 (2004) 801-805 www.elsevier.com/locate/expgero 

Hypothetical soluble KIR2DS4 natural killer cell receptor molecule does not associate with successful ageing in the Irish 

Owen A. Ross, Lynn D. Maxwell, I. Maeve Rea, Martin D. Curran 

a School of Biology and Biochemistry, Queen's University of Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, Northern Ireland, UK 
b Northern Ireland Regional Histocompatibility and Immunogenetics Laboratory, City Hospital, Belfast, Northern Ireland, UK 
c Department of Geriatric Medicine, Queen's University of Belfast, Belfast, Northern Ireland, UK 

Received 27 November 2003; received in revised form 14 January 2004; accepted 6 February 2004 

Abstract 
The identification of immunogenetic longevity markers is a major area of molecular gerontological research. A number of genetic loci have been examined, e.g. the HLA and cytokine networks. This study investigated a genetic marker within the highly polymorphic KIR gene system with successful ageing in the Irish population. A 22 bp deletion was identified in the KIR2DS4 gene that predicts a truncated soluble KIR molecule with one intact Ig-like domain. The frequency of this variant was determined using a specific-primer PCR methodology. There was no observed association between this common polymorphic variation within this activatory KIR gene and the aged Irish population. This is the first study of KIR polymorphism in ageing and although no association was identified, the importance of the KIR network in the immune response and its polymorphic nature warrants more detailed analysis to ascertain its role in immunosenescence. 

Keywords: KIR; 2DS4 deletion; Polymorphism; Ageing 

1. Introduction 
Elderly individuals maintain overall cytotoxic activity, even though there is an increased number of mature NK cells observed (Di Lorenzo et al., 1999; Solana et al., 1999; Miyaji et al., 2000). NK cells lyse abnormal cells that either lack the expression or express diminished amounts of human leukocyte antigen (HLA) class I molecules. 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 inhibitory receptors (Biassoni et al., 2000). With optimal functioning of the immune system, specific genetic determinants may reside in polymorphic loci that regulate the immune response. Dysregulation of immune function accompanying ageing (immunosenescence) is postulated to contribute to morbidity and mortality in the aged, via an increased risk of disease, infection, tumors, and autoimmune disorders (Franceschi et al., 1995, 2000; Solana and Pawelec, 1998; Malaguarnera et al., 2001). 

Human NK cells express two structurally distinct receptor families that mediate their interactions; the c-type lectin-like heterodimer receptors and the immunoglobulin-like (Ig-like) receptors (Lopez-Botet et al., 2000). In contrast to the relatively conserved CD94/NKG2 lectin-like receptors, the Ig-like receptors display considerable variation, particularly the killer cell immunoglobulin-like receptors (KIR). NK cells clonally express KIR genes and while it is unclear how the repertoire of receptors expressed by NK cells is created, recent studies on the NK cell expression of KIR in different individuals imply that the repertoire is dependent on the presence of different genes in an individual's genome (Uhrberg et al., 1997; Shilling et al., 2002). 

A hypothesis was proposed that a well-preserved NK cell activity is important for successful ageing (Sansoni et al., 1993; Franceschi et al., 1995; Shilling et al., 2002). The KIR gene family represents a highly polymorphic class of receptor-encoding genes, which to date have displayed considerable allelic diversity and it is postulated that KIR polymorphism arises from both the occurrence of random point mutations and recombination between homologous KIR genes (Shilling et al., 1998; Witt et al., 1999). This study aimed to ascertain whether this polymorphism within the KIR region was associated with successful ageing. 

2. Materials and methods 
Recently, our laboratory reported the presence of a common 22 bp deletion in the activatory KIR2DS4 gene that predicts a soluble KIR molecule (Maxwell et al., 2002). The deletion causes a frameshift predicting a truncated KIR2DS4 protein with a significantly altered D2 domain, which would be secreted due to the loss ofLanes 2 and 6 show the presence of the homozygous deleted 2DS4 form only. Lanes 3, 4, and 7 display the results for homozygous individuals displaying the full-length 2DS4 form only. The present study investigated the frequency of a common 22 bp deletion in the killer immunoglobulin-like receptor gene 2DS4 that predicts a soluble KIR molecule. A simple PCR methodology was employed to genotype 180 aged and 180 young control subjects from the Irish population. The observed frequencies of the deleted and full-length forms of the 2DS4 gene are displayed in Table 1.