Single nucleotide polymorphisms of cytokine genes in the healthy Slovak population

doi: 10.1111/j.1744-313X.2007.00693x

© 2007 The AuthorsJournal compilation © 2007 Blackwell Publishing Ltd, International Journal of Immunogenetics 34, 273–280 273

Blackwell Publishing LtdSingle nucleotide polymorphisms of cytokine genes in the healthy Slovak population

J. Javor,* M. Bucova,* S. Ferencik,† H. Grosse-Wilde† & M. Buc*

Summary

Cytokines are molecules that control and modulate theactivities of numerous target cells via binding to specificreceptors. The observed differences in the cytokineproduction among individuals can be, at least partially,explained by gene polymorphisms. Several cytokine genepolymorphisms have been identified to play a role insusceptibility to various diseases, including autoimmune,infectious, allergic or cardiovascular diseases.

The aim of the current study was to determine alleleand genotype frequencies of 22 polymorphisms in 13cytokine genes in the healthy Slovak population and tocompare them with data available from six populationsfrom Central and Southern Europe. A polymerase chainreaction with sequence-specific primers was used togenotype polymorphisms within genes encoding IL-1α,IL-1β, IL-1R, IL-1RA, IL-4Rα, IL-12, IFN-γ, TGF-β,TNF-α, IL-2, IL-4, IL-6 and IL-10 in a sample of 140unrelated Slovak subjects.

The allelic distribution of all polymorphisms in theSlovak population was very close to that in the geograph-ically and historically closest populations in CentralEurope — the Czech and the Polish. However, severaldifferences were found between the Slovak and fourpopulations from Southern Europe. The obtained datarepresent a basis for further studies on association ofcytokine gene polymorphisms with some diseases.

Introduction

Cytokines are proteins or glycoproteins that exert anumber of functions in immune and inflammatoryreactions. Their production is complex, coordinated andflexible and the disruption of the complex cytokinenetwork has been found in numerous immune-mediateddiseases, including autoimmune or infectious diseases

(Bidwell et al., 1999; Hunt et al., 2000). The observeddifferences in cytokine production and response tovarious antigens among individuals are caused by numer-ous factors, including gene polymorphisms. From amongseveral types of polymorphisms present in the humangenome, single nucleotide polymorphisms (SNPs) areby far the most frequent type (Weiner & Hudson, 2002;Thomas & Cann, 2003). Numerous SNPs in cytokinegenes have been identified, and some of them are associ-ated with qualitative or quantitative changes in proteinproduction and susceptibility to various diseases, includ-ing autoimmune, infectious, allergic or cardiovasculardiseases (for review see: Bidwell et al., 1999, 2001; Haukimet al., 2002; Hollegaard & Bidwell, 2006). Distributionof cytokine gene polymorphisms may vary significantlyamong different ethnic groups, what could eventuallycontribute to observed differences in disease frequencies.This fact has to be taken into consideration when usingan association analysis for detecting gene polymor-phisms that contribute to susceptibility or resistance tomultifactorial diseases. Case-control studies have the dis-advantage that a false-positive association can be observedwhen there are differences in genetic backgrounds be-tween patients and controls (Tsuchiya et al., 2002).

The aim of our study was to evaluate frequencies ofalleles, genotypes and haplotypes of selected cytokinegene polymorphisms in the Slovak population, as well asto compare the allele frequencies in our population withthose in some other European populations. The obtaineddata can be further used as a basis for studying diseaseassociations.

Materials and methods

Subjects

A total of 140 unrelated healthy Slovak subjects ofCaucasian origin, 66 men and 74 women (the median agewas 38 years, range 21–80), were randomly selected andincluded in this study. Their informed consent as wellas Comenius University ethics committee approval wasobtained before the study started.

DNA extraction

Genomic DNA was isolated automatically from 2 mLperipheral blood with chemagic Magnetic Separation

* Department of Immunology, School of Medicine, Comenius University, Bratislava, Slovakia and † Institute of Immunology, University Hospital of Essen, Essen, Germany

Received 5 April 2007; revised 5 April 2007; accepted 16 April 2007

Correspondence: Juraj Javor, MD, Department of Immunology, School of Medicine, Comenius University, Sasinkova 4, 811 08 Bratislava, Slovakia. Tel: +421 2 5935 7582; Fax: +421 2 5935 7578; E-mail: [email protected]

274 J. Javor et al.

© 2007 The AuthorsJournal compilation © 2007 Blackwell Publishing Ltd, International Journal of Immunogenetics 34, 273–280

Module I using the chemagic DNA Blood2k Kit (chemagenBiopolymer-Technologie Ag, Baesweiler, Germany).

Cytokine genotyping

Cytokine gene polymorphisms were determined bypolymerase chain reaction with sequence-specific primers(PCR-SSP) using the Cytokine Genotyping Kit (DynalBiotech, Invitrogen Corporation, Brown Deer, WI, USA),allowing us to determine alleles and genotypes of these22 single nucleotide polymorphisms within 13 cytokinegenes: IL-1α –889 (T/C), IL-1β –511 (T/C), IL-1β +3962(T/C), IL-1R pst1 1970 (T/C), IL-1RA mspa1 11100 (T/C), IL-4Rα +1902 (G/A), IL-12 –1188 (C/A), IFN-γ +874(A/T), TGF-β codon 10 (C/T), TGF-β codon 25 (G/C),TNF-α –308 (A/G), TNF-α –238 (A/G), IL-2 +166 (G/T),IL-2 –330 (T/G), IL-4 –1098 (T/G), IL-4 –590 (T/C), IL-4–33 (T/C), IL-6 –174 (C/G), IL-6 nt565 (G/A), IL-10–1082 (G/A), IL-10 –819 (C/T) and IL-10 –592 (A/C).The lyophilized primer mixes and reagents containedin the kit were developed by University of Heidelbergfor the cytokine polymorphism component of the 13thInternational Histocompatibility Workshop (Seattle,USA, 2002). More information on the primers andtheir accuracy can be found at http://www.ihwg.org/components/cytokine/cytover.htm. PCR amplificationwas carried out exactly according to manufacturer’smanual using a PTC-100 and PTC-200 Thermal Cycler(MJ Research, Inc., Waltham, MA, USA).

Statistical analysis

Allele, genotype and haplotype frequencies were calcu-lated by direct counting and then dividing by the numberof subjects (to produce genotype frequency) or chromo-somes (to produce allele and haplotype frequency).Furthermore, observed and expected frequencies ofthe various genotypes were compared using the χ2 testwith one degree of freedom to test for their fit to Hardy–Weinberg equilibrium (HWE). The Fisher’s exact test wasused to compare allele frequencies in the Slovak popula-tion with those in other populations. The P-values werecorrected for the number of comparisons according toBonferroni. The differences were considered statisticallysignificant when a corrected two-sided P-value was lessthen 0.05. The analysis was performed using instatstatistical software (GraphPad Software, Inc., San Diego,CA, USA). The program gendist available in the phylippackage (Felsenstein, 2002) was used to compute distancedata from allele frequencies in 16 populations. Theconstruction of phylogenetic tree from distance matriceswas then performed by mega 3.1 software (Kumar et al.,2004) using the neighbour-joining method of Saitou andNei (1987).

Results

The allele and genotype frequencies of cytokine genepolymorphisms in the Slovak population are given in

Table 1, and the haplotype frequencies are reported inTable 2. The genotype frequency distribution of allstudied polymorphic cytokine genes followed the Hardy–Weinberg distribution and no deviation from HWE wasobserved (Table 1). By comparison of allele frequencies inthe Slovak population with data available from some otherEuropean Caucasian populations — Czech (Cinek et al.,2004), Italian (Uboldi de Capei et al., 2003), Macedonian(Trajkov et al., 2005), Polish (Kurzawski et al., 2005),Bulgarian (Mihailova et al., 2005) and Greek-Cypriot(Costeas et al., 2003), some significant differences werefound (Table 3).

Initially, we compared the allele distribution of 22cytokine gene polymorphisms in our population withpublished data from two neighbouring populations ofCentral Europe. The cytokine frequencies observed inthe Slovak population were similar to those found in theCzech population, and although slight differences in allelefrequencies of IL-1β +3962 (T/C), TGF-β codon 10 (C/T)and IL-6 –174 (C/G) polymorphisms were observed, theywere not statistically significant (Table 3). These resultsare not surprising since both Slovaks and Czechs belongto closely related Slavonic populations with similar history.The comparison of allelic frequencies with anotherSlavonic population of Central Europe, the Polish popu-lation, was limited since data on seven polymorphismswithin five cytokine genes (TNF, IL-2, IL-4, IL-6 and IL-10) were available only. Increased frequency of upregulat-ing G allele of IL-6 –174 SNP (61.4% vs. 53.4%) wasfound in the Slovak population; however, this differencelost its statistical significance after the correction by theBonferroni’s method. The allelic distribution for theremaining six cytokine polymorphisms did not differ sig-nificantly between the Slovak and the Polish population.

Since no data from populations of other neighbouringstates were available, we further compared the allelefrequencies in Slovaks with those from four SouthernEuropean populations: the Slavonic populations ofMacedonia and Bulgaria, as well as the Italian and Greek-Cypriot populations (Table 3). By comparing the Slovakand Italian populations, a significantly increased frequencyof the less common T allele of IL-2 +166 SNP (37.0% vs.22.5%, Pc < 0.01) was observed in the Slovak population.The distribution of remaining 21 cytokine SNP alleles didnot differ significantly between the two populations. Sur-prisingly, more differences were observed when the Slovakand Macedonian population were compared. The allelicfrequencies of six polymorphisms: IL-1α –889 (T/C),TGF-β codon 25 (G/C), IL-2 –330 (T/G), IL-2 +166 (G/T),IL-6 –174 (C/G) and IL-6 nt565 (G/A) varied betweenthem, but only the differences in allele frequencies ofIL-1α –889 (T/C) and IL-2 +166 (G/T) polymorphismsremained significant after the Bonferroni’s correction(IL-1α –889 C allele: 74.5% in Slovaks vs. 91.4% in Mac-edonians, Pc < 0.01; IL-2 +166 G allele: 63.0% vs. 77.9%,Pc < 0.01). It is worth mentioning that fewer differencesappeared between the Macedonian population and theItalian population, which is not of Slavonic origin. Finally,we also evaluated the differences between the Slovak and

http://www.ihwg.org/components/cytokine/cytover.htm

Cytokine gene polymorphisms in Slovaks 275


Cytokine polymorphism Allele N % Genotype N %

HWP P-value

IL-1α –889 C 204 74.45 CC 76 55.47 0.9310T 70 25.55 CT 52 37.96

TT 9 6.57IL-1β –511 C 195 69.64 CC 69 49.29 0.6651

T 85 30.36 CT 57 40.71TT 14 10.00

IL-1β +3962 C 209 74.64 CC 81 57.86 0. 1774T 71 25.36 CT 47 33.57

TT 12 8.57IL-1R pst1 1970 C 174 62.14 CC 53 37.86 0.7042

T 106 37.86 CT 68 48.57TT 19 13.57

IL-1RA mspa1 11100

C 97 34.64 CC 21 15.00 0.1133T 183 65.36 CT 55 39.29

TT 64 45.71IL-4Rα +1902 A 211 76.45 AA 82 59.42 0.5319

G 65 23.55 AG 47 34.06GG 9 6.52

IL-12 –1188 A 215 77.34 AA 85 61.15 0.6289C 63 22.66 AC 45 32.37

CC 9 6.48IFN-γ +874 A 149 53.21 AA 41 29.28 0.6506

T 131 46.79 AT 67 47.86TT 32 22.86

TGF-β codon 10 C 125 44.96 CC 27 19.42 0.7073T 153 55.04 CT 71 51.08

TT 41 29.50TGF-β codon 25 C 22 7.91 CC 0 0.00 0.3121

G 256 92.09 CG 22 15.83GG 117 84.17

TNF-α –308 A 37 13.21 AA 3 2.14 0.6856G 243 86.79 AG 21 22.14

GG 106 75.72TNF-α –238 A 11 3.93 AA 0 0.00 0.6344

G 269 96.07 AG 11 7.86GG 129 92.14

IL-2 –330 G 87 31.52 GG 16 11.59 0.6297T 189 68.48 GT 55 39.86

TT 67 48.55IL-2 +166 G 174 63.04 GG 56 40.58 0.6776

T 102 36.69 GT 62 44.93TT 20 14.49

IL-4 –1098 G 23 8.21 GG 1 0.71 0.9488T 257 91.79 GT 21 15.00

TT 118 84.29IL-4 –590 C 229 81.79 CC 94 67.14 0.8347

T 51 18.21 CT 41 29.29TT 5 3.57

IL-4 –33 C 229 81.79 CC 94 67.14 0.8347T 51 18.21 CT 41 29.29

TT 5 3.57IL-6–174 C 108 38.57 CC 21 15.00 0.9502

G 172 61.43 CG 66 47.14GG 53 37.86

IL-6 nt565 A 103 36.79 AA 18 12.86 0.7314G 177 63.21 AG 67 47.86

GG 55 39.28IL-10 –1082 A 159 56.79 AA 49 35.00 0. 1812

G 121 43.21 AG 61 43.57GG 30 21.43

IL-10 –819 C 205 73.21 CC 77 55.00 0.5956T 75 26.79 CT 51 36.43

TT 12 8.57IL-10 –592 A 75 26.79 AA 12 8.57 0.5956

C 205 73.21 AC 51 36.43CC 77 55.00

N, number of alleles and genotypes; HWP, Hardy–Weinberg proportions.

Table 1. Allele and genotype frequencies in the Slovak population

276 J. Javor et al.


two other Southern European populations — the Bulgarianand the Greek-Cypriot. However, the data available fromthese populations were limited to eight polymorphisms infive cytokine genes only (Table 3). The distribution ofvariants within IFN-γ, TNF-α, TGF-β and IL-6 genes inthe Bulgarian population was very close to that in theSlovak population, and differences occurred in three IL-10 polymorphisms only, caused by overexpression of–1082 A, –819 T and –592 A alleles in Bulgarians.However, only the difference in allelic distribution ofSNP at position –819 remained significant after thecorrection (the frequency of T allele was 26.8% in Slovaksvs. 40.7% in Bulgarians; Pc < 0.05). It is quite interestingthat similar differences also appeared when the Bulgarianpopulation was compared with other populations. Finally,the cytokine gene polymorphisms in the Greek populationof Cyprus showed similar allelic distribution to those inSlovaks, with exception of IL-6 –174 (C/G) SNP, where asignificantly increased frequency of G allele in Greek-Cypriots was observed (61.4% vs. 81.5%, Pc < 0.001).

To further extend our comparisons, we have alsoinvestigated differences in allelic distribution betweenthe Slovak and several other European and especiallynon-European populations. The results obtained havebeen used to construct a phylogenetic tree illustratingrelationships between the populations compared. Thecytokine genotyping in all 16 populations shown in thephylogenetic tree was performed by the same PCR-SSPmethod using either the ‘Heidelberg’ kit (CytokineCTS-PCR-SSP Tray Kit, University of Heidelberg, Heidel-berg, Germany, http://www.ihwg.org) or the commercialversion Cytokine Genotyping Kit (Dynal Biotech, Invitro-gen Corporation) (Louie et al., 2004; Trejaut et al., 2004;Bagheri et al., 2006; Kubistova et al., 2006; Skorpil et al.,2007). The cytokine phylogenetic tree (Fig. 1) shows arather high degree of genetic similarity between European

populations, and a greater diversity in cytokine genepolymorphisms occurred between Europe, Asia andMiddle or South America.

Discussion

Cytokines are small proteins or glycoproteins producedby a wide range of cell types as a response to antigen-specific or non-antigen-specific stimuli and exert a numberof functions in immune and inflammatory reactions. Theirproduction is complex, coordinated and flexible, and thedisruption of this complex network has been observed innumerous immune-mediated diseases (Bidwell et al., 1999;Hunt et al., 2000). Since polymorphisms (mostly SNPs)located within critical promoter or other regulatory regionsmay affect gene transcription resulting in variations incytokine production levels, the observed differences in themagnitude and profile of cytokine response to variousstimuli appear to be, at least in part, due to these polymor-phisms (Bidwell et al., 1999; van Deventer, 2000). Toreveal the possible role of cytokine gene polymorphisms indisease pathogenesis, a considerable amount of functionaland association studies has been done. Some of them haveprovided important evidence for the influence of polymor-phisms on disease susceptibility, onset, course, response todrug therapy or post-transplant outcome (Bidwell et al.,1999; Hoffmann et al., 2001).

In this study, we describe the allele frequencies of22 polymorphisms located in genes of 13 pro- or anti-inflammatory cytokines, including IL-1α, IL-1β, IL-1R,IL-1RA, IL-4Rα, IL-12, IFN-γ, TGF-β, TNF-α, IL-2,IL-4, IL-6 and IL-10. Most of the examined polymorph-isms are of functional relevance, although some of thefunctional studies provided ambiguity (Table 4).

Initially, we compared our results on allele frequencieswith data available from geographically and ethnically

Table 2. Haplotype frequencies in the Slovak population

Cytokine polymorphism HaplotypeNumber (N )

Frequency (%)

TGF-β codon 10 and 25 TG 153 55.04CG 103 37.05CC 22 7.91

TNF-α –308 and –238 GG 232 82.86AG 37 13.21GA 11 3.93

IL-2 –330 and +166 TT 102 36.96TG 87 31.52GG 87 31.52

IL-4 –1098, –590 and –33 GCC 23 8.21TCC 206 73.58TTT 51 18.21

IL-6 –174 and nt565 CA 106 37.86CG 5 1.79GG 172 61.43

IL-10 –1082, –819 and –592 GCC 121 43.21ACC 84 30.00ATA 75 26.79

Figure 1. Phylogenetic tree generated from cytokine gene distance data from 16 populations.

http://www.ihwg.org



closest Central European populations — the Czech (Cineket al., 2004) and the Polish (Kurzawski et al., 2005). Dueto the proximity of these populations, it was not surprisingthat no significant differences in allelic distribution amongthem were observed, thus possibly reflecting a high degreeof homogeneity in Central European populations.Furthermore, we compared our data with those reportedfrom populations of Southern Europe — Italian (Uboldide Capei et al., 2003), Macedonian (Trajkov et al., 2005),Bulgarian (Mihailova et al., 2005) and Greek-Cypriot(Costeas et al., 2003). Although the data available from

both Bulgarians and Greek-Cypriots were restricted toeight SNPs within five cytokine genes, we found somedifferences between the Slovak and all four SouthernEuropean populations. However, the significant differ-ences were limited only to one or two polymorphisms percomparison (IL-1α –889, IL-2 +166, IL-6 –174 or IL-10–819 SNP), and the allelic distribution of the remainingmajority of SNPs was similar. Ethnicity is clearly associatedwith more dramatic differences in cytokine polymorphismdistribution, since numerous studies found statisticallysignificant variations in allelic frequencies of several cytokine

Table 3. Comparison of allele frequencies in the Slovak, Czech, Italian, Macedonian, Polish, Bulgarian and Greek-Cypriot populations

Cytokine polymorphism Allele

Population (%)

Slovak n = 140

Czech n = 103

Italiann = 140

Macedonian n = 125

Polish n = 225

Bulgariann = 86

Greek-Cypriot n = 100

IL-1α –889 C 74.5 76.0 71.4 91.4b — — —T 25.5 24.0 28.6 8.6 — — —

IL-1β –511 C 69.6 74.8 70.7 64.8 — — —T 30.4 25.2 29.3 35.2 — — —

IL-1β +3962 C 74.6 66.2 74.3 68.4 — — —T 25.4 33.8 25.7 31.6 — — —

IL-1R pst11970 C 62.1 63.1 66.8 64.4 — — —T 37.9 36.9 33.2 35.6 — — —

IL-1RA mspa1 11100 C 34.6 34.0 23.2 27.6 — — —T 65.4 66.0 76.8 72.4 — — —

IL-4Rα +1902 A 76.4 74.3 81.4 82.4 — — —G 23.6 25.7 18.6 17.6 — — —

IL-12 –1188 A 77.3 77.8 72.5 70.3 — — —C 22.7 22.2 27.5 29.7 — — —

IFN-γ +874 A 53.2 50.0 53.6 49.3 — 51.2 47.5T 46.8 50.0 46.4 50.7 — 48.8 52.5

TGF-β codon 10 C 45.0 37.4 45.4 50.9 — 47.1 42.5T 55.0 62.6 54.6 49.1 — 52.9 57.5

TGF-β codon 25 C 7.9 7.8 7.9 3.3 — 8.7 7.0G 92.1 92.2 92.1 96.7 — 91.3 93.0

TNF-α –308 A 13.2 — 9.3 13.2 14.9 14.0 7.5G 86.8 — 90.7 86.8 85.1 86.0 92.5

TNF-α –238 A 3.9 — 7.5 8.0 — — —G 96.1 — 92.5 92.0 — — —

IL-2 –330 G 31.5 33.2 33.9 40.5 35.1 — —T 68.5 66.8 66.1 59.5 64.9 — —

IL-2 +166 G 63.0 68.3 77.5b 77.9b — — —T 37.0 31.7 22.5 22.1 — — —

IL-4 –1098 G 8.2 12.7 8.9 9.1 — — —T 91.8 87.3 91.1 90.9 — — —

IL-4 –590 C 81.8 85.3 88.6 84.5 79.8 — —T 18.2 14.7 11.4 15.5 20.2 — —

IL-4 –33 C 81.8 85.3 86.4 84.9 — — —T 18.2 14.7 13.6 15.1 — — —

IL-6 –174 C 38.6 45.1 34.3 29.2 46.6 36.6 18.5c

G 61.4 54.9 65.7 70.8 53.4 63.4 81.5IL-6 nt565 A 36.8 41.7 33.2 28.4 — — —

G 63.2 58.3 66.8 71.6 — — —IL-10 –1082 A 56.8 54.9 60.7 63.0 55.9 68.6 62.0

G 43.2 45.1 39.3 37.0 44.1 31.4 38.0IL-10 –819 C 73.2 70.9 72.1 72.3 76.1 59.3a 76.5

T 26.8 29.1 27.9 27.6 23.9 40.7 23.5IL-10 –592 A 26.8 29.1 27.9 27.6 23.9 38.4 23.5

C 73.2 70.9 72.1 72.3 76.1 61.6 76.5

n, number of individuals tested; ––, data not found; corrected P-values: a Pc < 0.05; b Pc < 0.01; c Pc < 0.001.

278 J. Javor et al.


gene polymorphisms among different ethnic groups (Whites,Blacks, Hispanics and Asians) (Hoffmann et al., 2002;Pyo et al., 2003; Ness et al., 2004; Trejaut et al., 2004).Therefore, we also investigated the differences in allelicdistribution of 22 cytokine SNPs between several otherEuropean and non-European populations and used thedistance data to construct a phylogenetic tree that illu-strates relationships between populations. The cytokinephylogenetic tree shows that the distribution of cytokinealleles is similar between European populations, andmajor splits can be observed between Europe, Asia andMiddle or South America. And although more polymorphicgenetic systems (e.g. HLA) would be more suitable forconstructing phylogenetic trees with high discriminatorypower, cytokines analysis might still provide some usefulinformation when tracing relationships between popula-tions. The observed racial variations may be of greatimportance as the collective influence of several cytokinesand their polymorphisms could affect immune responsesas complex. Therefore, the differences in cytokine allelicfrequencies could lead to different secretory profiles,responses to stimuli and susceptibility to diseases. Apossible explanation of these differences is a naturalevolutionary selection, increasing the frequency of mostadvantageous alleles and genotypes. Thus, allele frequen-cies of a particular cytokine polymorphism would repre-sent local adaptation to diverse pathogenic challenges.However, specific causes, such as environmental factors,which select some allelic forms in one population com-pared to other, remain mostly unclear. Moreover, animportant role of another basic mechanism of evolution— the genetic drift — should not be omitted, especially insmaller populations (Suzuki et al., 1989). Wirz et al. (2004)investigated allelic frequencies of TNF-α –238 and –376SNPs in Sicilian and Sardinian subjects. While alleles TNF–376 A and –238 A are normally found throughout theworld with very low frequencies, their frequencies inSardinia were elevated significantly in comparison toSicily and other populations throughout the world, possi-bly as a result of genetic drift or selective pressure on TNF

itself or on neighbouring genes. Malaria, endemic in Sar-dinia until the end of the 1940s, and the bubonic plagueare among the possible causes of selection. The authorssuggest that these differences in TNF (or adjacent HLA)allele frequencies could contribute to unusually highprevalence of multiple sclerosis and type 1 diabetes inSardinia (Wirz et al., 2004). Another example of naturalselection could be the IL-4 –590 (C/T) polymorphism.The –590 T allele is associated with higher transcrip-tional activity and higher IgE production in comparisonto the C allele. IgE production plays a crucial role in pro-tection against parasites, particularly helminths. Severalstudies observed significantly increased frequency ofthe T allele in Asian and African populations compared toEuropean Caucasian populations, possibly as a result ofselective pressure, since most helminths thrive in the trop-ical climate but struggle to reproduce in cooler or drier cli-mates. Since IgE plays also crucial role in the pathogenesisof allergic diseases, it is possible that increasing western-ization among the people living in the tropics will producerapidly increasing levels of asthma, as these populationshave a high genetic predisposition to allergic disease(Rockman et al., 2003; Le Souëf et al., 2006).

In conclusion, analysis of allele distributions of selectedcytokine gene polymorphisms in the Slovak populationhas shown that these are generally similar to those foundin other European Caucasian populations, and althoughsome significant differences occurred, especially betweenour population and the Southern European population,these were limited to few polymorphisms only. Thestudies on distribution of cytokine gene polymorphismswithin populations may be a helpful tool to examinerelationships between populations and to understandobserved differences in cytokine secretion profiles andresponses to various stimuli among populations. They canfurther become a basis for the research on associationsbetween cytokine polymorphisms and various immuno-logical phenomena, including infectious and cardiovasculardiseases, cancer, autoimmune disorders or transplantreactions.

Allele Functional effects References

IL-1α –889 T Higher IL-1α production Dominici et al. (2002)Hulkkonen et al. (2000)

IL-1β +3962 T Higher IL-1β production Pociot et al. (1992)IL-2 –330 G Higher IL-2 production Hoffmann et al. (2001)IL-4 –590 T Higher transcriptional activity Rosenwasser et al. (1995)

Higher IgE productionIL-4Rα +1902 G Prolongated signalling activity

of the variant receptorPan & Rothman (1999)

IL-6 –174 G Higher transcriptional activity Fishman et al. (1998)IL-10 –1082 G Higher IL-10 production Turner et al. (1997)TNF-α –308 A Higher TNF-α production Kroeger et al. (1997)

Wilson et al. (1996)IFN-γ +874 T Higher IFN-γ production Hoffmann et al. (2001)

Pravica et al. (2000)TGF-β codon 10 T Higher TGF-β production Awad et al. (1998)TGF-β codon 25 G Higher TGF-β production Awad et al. (1998)

Table 4. Functional effects of cytokine gene polymorphisms



Acknowledgements

The authors wish to thank Mrs M. Praast and Mrs M.Piatkova for their technical assistance. This study wassupported by the Research Program of the Ministry ofEducation of the Slovak Republic VEGA 1/3437/06,Comenius University Grant UK/25/2006 and Short-TermFellowship of European Federation of ImmunologicalSocieties.

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Single nucleotide polymorphisms of cytokine genes in the healthy Slovak population