Natural Killer Cells from HIV Infected Slow Progressors Who Carry the Protective HLA-B*27 Allele and Inhibitory KIR3DL1 Receptors Have Elevated Poly-Functional Potential Compared to Bw6 Homozygotes

Nicole F. Bernard1,2,3,10 et al.* for the Canadian Cohort of HIV Infected Slow Progressors 1Research Institute of the McGill University Health Centre 2Division of Experimental Medicine, McGill University, Clinique du Quartier 3Division of Clinical Immunology and Allergy, McGill University Health Centre, Toronto, Ontario 10Centre de Recherche du Centre Hospitalier de l’Universite de Montreal Montreal, Quebec, Canada


Introduction
NK cells are a key component of the innate immune system, which can act early in defences against virally infected and tumor cells (Robertson and Ritz 1990;Bottino, Moretta, and Moretta 2006;Bancroft 1993).They have the capacity to secrete proinflammatory cytokines and lyse their targets without prior antigen sensitization (Cooper, Fehniger, and Caligiuri 2001).They are also involved in regulation of the adaptive immune response through their interaction with dendritic cells (DCs) (Sanabria et al. 2008;Smyth et al. 2005).
Natural Killer Cells from HIV Infected Slow Progressors Who Carry the Protective HLA-B*27 Allele and Inhibitory KIR3DL1 Receptors Have Elevated... 195 example in humans of an MHC class I antigen with an NK education potency that is superior to that of most other HLA-Bw4 molecules.HLA-B*27 is another allele considered to be protective in the context of HIV infection (Kaslow et al. 1996;Carrington and Bontrop 2002;Goulder, Edwards et al. 1997;Trachtenberg et al. 2003).Like HLA-B*57, its protective effect is medi ated at least i n part through immune pressure exerted by CD8 + T cells (Schneidewind et al. 2009;Goulder, Phillips et al. 1997;den Uyl, van der Horst-Bruinsma, and van Agtmael 2004;Goulder et al. 2001).In this report we questioned whether HLA-B*27, like HLA-B*57, could also act as a ligand for 3DL1 NK receptors that was superior to other HLA-Bw4 alleles in terms of its ability to educate NK cells for functional potential.HLA-B*27 is found at a higher frequency among the approximately 5% of HIV infected individuals that we have classified as Slow Progressors (SP) compared with HIV infected individuals exhibiting a typical rate of disease progression or uninfected subjects (Carrington, Martin, and van Bergen 2008;Kaslow, Dorak, and Tang 2005).SP are defined by either exhibiting spontaneous control of viremia or maintaining CD4 counts >400 cells/mm3 for at least 7 years post-infection (Madec et al. 2005;Deeks and Walker 2007).In order to determine whether HLA-B*27, like HLA-B*57, could educate NK cells from 3DL1 hmz individuals for superior functional potential we compared the functional potential of NK cells from 3DL1 hmz+B*27 (3DL1+B*27) carriers with that from 3DL1 hmz who were Bw6 hmz ( 3DL1+Bw6) or who expressed at least 1 Bw4 alleles other than B*57 or B*27 (3DL1+Bw4).NK cells from 3DL1+B*27 carriers had a significantly higher functional potential than those from 3DL1+Bw6.When the functional potential of NK cells from carriers of the 3DL1 NK receptor /HLA-B ligand pairs *h/*y+B*57, 3DL1+B*27 and 3DL1+Bw4 were compared we observed decreasing levels in the functional potential where NK cells responded to missing self with a h/*y+B*57 > 3DL1+B*27 > 3DL1+Bw4 hierarchy.

Study population
A total of 51 HIV-infected SP were studied.Forty four were from the Canadian Cohort of HIV Infected Slow Progressors and 7 were from a cohort followed at the National Institutes of Allergy and Infectious Diseases (NIAID) (Migueles et al. 2008).The term SP was used here to define treatment naïve HIV infected subjects who maintained absolute CD4 counts above 400 cells/mm 3 for more than 7 years or who were followed for at least 1 year with VL <3000 copies/ml of plasma.Information on CD4, CD8 T cell counts, VL and duration of infection at time of testing, 3DL1 genotype and HLA-B allotype of the study population is provided in Table 1.All individuals in the study populations are 3DL1 hmz to eliminate the possible confounding effect on NK function of expressing the activating 3DS1 receptor, which is an allele at this locus (Martin et al. 2007;Boulet et al. 2008;Yawata et al. 2006).The study population is classified into 4 groups: group 1 (n=12) carry the 3DL1+B*27 genotype, group 2 (n=13) are 3DL1+Bw4, group 3 (n=14) are 3DL1+Bw6 and group 4 (n=12) are *h/*y+B*57.Informed consent was obtained from all study subjects and research conformed to the ethical guidelines of the authors' institutions.

MHC and KIR typing
All subjects were typed for MHC class I alleles by sequence-based typing using kits from Atria Genetics (South San Francisco, CA) and Assign software to interpret sequence information for allele typing (Conexio Genetics, Perth, Australia) as previously described (Boulet et al. 2010).HLA-Bw6 hmz subjects lacked any HLA-Bw4 alleles at the HLA-A or B locus.3DL1/S1 genotyping was performed using two sets of primers specific for the 3DL1 and 3DS1 alleles at the 3DL1 locus as previously described (Boulet et al. 2008).Subjects were subsequently 3DL1 allotyped by identifying single nucleotide polymorphisms (SNP) corresponding to high frequency 3DL1 alleles as previously described (Boulet et al. 2010)

NK cell functional potential
Cryopreserved PBMC were thawed and resuspended at 10 6 cells/ml in RPMI 1640 (Wisent) that contained 10% FBS (Wisent), 2mM L-glutamine and 50 IU penicillin and 50µg/ml streptomycin (Wisent).Brefeldin A (at 5µg/ml, Sigma-Aldrich), Monensin (at 6µg/ml, Golgi-Stop; BD Biosciences, Mississauga, Ontario, Canada) and anti-CD107a-FITC mAb (BD Biosciences) were added to the cells.One million PBMCs were stimulated with media alone or HLA devoid K562 cells (American Type Culture Collection Manassas, VA) at a PBMC to K562 cell ratio of 5:1 or with 1.25µg/ml phorbol 12-myristate 13-acetate (PMA); 0.25µg/ml ionomycin, (Sigma-Aldrich) as a positive control for 6 hours at 37 o C in a humidified 5% CO 2 incubator.All stimulation data shown is from cells that generated a positive result in the PMA and ionomycin stimulation condition.Cells were stained for viability using the Aqua LIVE/DEAD ® fixable dead cell stain kit (Invitrogen, Burlington, Ontario, Canada) following manufacturer's instructions.Cells were then stained for cell surface markers with anti-CD56-APC, anti-CD16-Pacific Blue (BD Biosciences), anti-CD3-ECD and CD158e-PE (ie: Z27-PE, Beckman Coulter, Mississauga, Ontario, Canada) for 30 min.After washing with phosphate buffered saline (PBS) containing 1% FBS (Wisent), cells were fixed and permeabilized using the Fix and Perm Kit (Invitrogen) and stained for intracellular cytokines using anti-IFN--Alexa 700 and anti-TNF--PE-Cy7 (BD Biosciences).Cells were washed and fixed with 1% paraformaldehyde solution (Fisher Scientific, Ottawa Ontario, Canada) and kept in the dark at 4 o C until acquisition.

Flow cytometry analysis
Between 400,000 and 500,000 events were acquired per sample using an LSRII flow cytometer (BD Biosciences).Analysis for NK cell activation was performed using FlowJo software version 9.1 (Tree Star, San Carlos, CA).The functional profiles of stimulated NK cells were determined using a gating strategy where NK cells were defined as CD3 -CD56 +/- CD16 +/-.Boolean gating was used to identify seven NK cell functional profiles, i.e. trifunctional NK cells (CD107a + IFN- + TNF- + ), bi-functional NK cells (any combination of two of these functions) and mono-functional NK cells (any single one of these functions).All results for the frequency of individual functional subsets were background corrected by subtracting the frequency of positive NK cells in the unstimulated subset.Corrected results were used to generate the percent contribution of each functional subset to the total NK cells response to K562.Results reported as subset frequency or percent contribution of a subset to the total K562 response showed a high level of correlation with each other (Boulet et al. 2010).

Statistical analysis
GraphPad Instat 3.05 and GraphPad Prism 5.04 were used for statistical analyses and graphical presentations.A Kruskal-Wallis test was used to assess the significance of between group differences in age, duration of infection at the time point tested, CD4 counts, CD8 counts and VL.Mann-Whitney U tests were used to test the significance of between group differences in the percent contribution of an NK cell functional subset to the total NK cell response.A Spearman correlation test was used to test the significance of the trend towards declining tri-functional potential with 3DL1/HLA-B genotype combinations.A p value of <0.05 was considered significant.
Since we simultaneously measured these three functions following K562 stimulation we were able to assess the frequency of seven possible NK cell functional profiles and their percent contribution to the total K562 response.Figure 1B shows the percent contribution of each NK cell functional profile in PBMC from 12 3DL1+B*27 and 14 3DL1+Bw6 subjects.Of the seven possible NK cell functional profiles, only the percent contribution of tri-functional NK cells to the total K562 response was significantly higher in the  2A).

202
3DL1 hmz genotypes can be classified as either *h/*y or *l/*x depending on the 3DL1 alleles expressed.Previous work showed that NK cells from *h/*y+B*57 subjects had a significantly higher tri-functional potential than those from *l/*x+B*57 subjects.We therefore questioned whether NK cells from the 7 *h/*y+B*27 and 5 *l/*x+B27 individuals differed from each other in their tri-functional potential.The median (range) NK tri-functional potential was 2.56% (0.00%, 6.18%) and 3.57% (0.47%, 6.43%) for NK cells from carriers of the *h/*y+B*27 and *l/*x+B*27 genotypes, respectively (p=0.53;Mann-Whitney test), a difference that was not statistically significant (Figure 2B).Therefore, HLA-B*27 appears to be able to interact with NK receptor alleles in either the 3DL1 *h/*y and *l/*x genotype categories to educate NK cells for equivalent NK functional potential.

NK cells from 3DL1+B*27 and *h/*y+B*57 carriers have a similar tri-functional potential
Next we questioned whether the level of tri-functional potential of NK cells from 3DL1+B*27 carriers was of a similar magnitude to that seen in NK cells from *h/*y+B*57 carriers.For this analysis we excluded the 2 3DL1+B*27 individuals who also expressed a B*57 allele and compared NK tri-functional potential in this group to that in 12 *h/*y+B*57 carriers.As seen in Figure 3A, although the tri-functional potential of NK cells from *h/*y+B*57 carriers was h i g h e r t h a n t h a t f r o m 3DL1+B*27 carriers this difference did not achieve statistical significance (p=0.09;Mann-Whitney test).Pair-wise comparisons of the tri-functional potential of NK cells from carriers of *h/*y+B*57, 3DL1+B*27 and 3DL1+Bw4 revealed that only the comparison of *h/*y+B*57 and 3DL1+Bw4 was statistically significant.NK cells from each of these groups had higher tri-functional potential than those from the 3DL1+Bw6 group (not shown).Small group sizes and large variability within groups likely contributed to the lack of statistical significance in the tri-functional potential between the *h/*y+B*57 and 3DL1+B*27 and the 3DL1+B*27 and 3DL1+Bw4 groups.We performed another analysis testing for the significance of a trend towards declining NK functional potential among subjects with these 3DL1/HLA-B genotypes.The rationale for this came from epidemiological studies showing that the effect of B*57 on time to AIDS and VL control was greater in the presence of *h/*y than *l/*x 3DL1 genotypes and greater than that of B*27 on these outcomes in the presence of either 3DL1 genotype (Martin et al. 2007).When the trifunctional potential of NK cells from these 3 3DL1/HLA-B genotypes were assessed.Using a test of trend we observed that this measure decreased as follows: *h/*y+B*57 > 3DL1+B*27 > 3DL1+Bw4 (r=-0.40,p=0.01;Spearman's correlation test).Together these results suggest that there is a hierarchy in the impact on NK cell education of HLA-B variants where B*57 is the most potent in the context of *h/*y genotypes followed by B*27 in the context of 3DL1 genotypes.Furthermore the impact of these alleles is superior to that of other Bw4 alleles co-expressed with 3DL1 genotypes.

Discussion
We have presented results showing that NK cells from carriers of the 3DL1+B*27 KIR/HLA genotype combination have tri-functional responses to missing self that are 1) significantly higher than those from 3DL1+Bw6 and 2) have a tri-functional potential that falls between that of carriers of *h/*y+B*57 and 3DL1+Bw4.We previously showed that B*57 is superior to most other Bw4 alleles in educating NK cells through its interaction with 3DL1 NK receptors for functional potential as measured by responses to missing self on K562 cells (Boulet et al 2010;Kamya et al. 2011).These results suggested that B*57, an allele associated with slow time to AIDS and VL control, may contribute to viral control not only through its interaction with HIV epitopes recognized by CD8 + T cell but also through its interaction with 3DL1 inhibitory receptors on NK cells.B*27 is another allele associated with slow time to AIDS and VL control.We therefore sought to determine whether B*27 was also able to educate NK cells for potent www.intechopen.comHIV Infection in the Era of Highly Active Antiretroviral Treatment and Some of Its Associated Complications 204 responses to missing self.The rationale for investigating the role of B*27 in educating NK cells for NK functional potential in HIV infected SP is that this allele is over represented among SP compared to the uninfected or HIV susceptible subjects.Among 101 SPs enrolled in the Canadian Cohort of HIV Infected SP typed to date 18 (17.8%)were B*27 positive whereas in HIV susceptible subject enrolled in a Primary HIV Infection cohort 26 of 434 (6%) expressed this allele (p<0.001;Fisher's Exact test), an allele frequency similar to that seen in uninfected Caucasian (www.allelefrequencies.net).The frequency of individuals expressing both a B*27 allele and a homozygous 3DL1 genotype would be expected to be even lower.This provided the rationale for investigating this phenomenon in SPs in whom the frequency of the KIR/HLA genotype under investigation was higher than in uninfected subjects.We also reasoned that SPs with either controlled viremia or long term non progression would constitute a population with limited NK dysfunction due to HIV infection.Others have reported that HIV infection dysregulates NK cell subset distribution such that there is a reduction in the frequency of the CD56 + CD16 + NK subset with cytolytic activity with an associated increase the frequency of an anergic CD56 -/CD16 + subset (Mavilio et al. 2005;Tarazona et al. 2002).VL seems to play a key role in this redistribution of NK cell subsets.Even though a decrease of cytotoxic NK cells is observed in SPs compared to healthy controls it is not as pronounced as that observed in viremic HIV infected progressor subjects (O'Connor et al. 2007;Barker et al. 2007).NK function may be altered by direct contact with HIV.The gp120 Envelope glycoprotein has been shown to suppress the activity, proliferation and survival of NK cells (Kottilil et al. 2006).Perturbations in the NK cell receptor repertoire have been reported in HIV infection, affecting both inhibitory and activating receptors (Kottilil et al. 2004;Mavilio et al. 2003;De Maria et al. 2003;O'Connor et al. 2007).Furthermore, HIV can escape NK cell recognition by restricting upregulation of activating NK cell receptor ligands such as NKp44L (Fausther-Bovendo et al. 2009), MICA and ULBP1 and 2 (Cerboni et al. 2007) and by preventing downregulation of HLA-C/E (Bonaparte and Barker 2004).Results reported by Kamya et al. demonstrated a negative correlation between NK cell tri-functional potential and VL suggesting VL and HIV infection negatively impact NK function (Kamya et al. 2011).In summary, although NK function in SPs may be affected by HIV infection the effect would be expected to be limited in this population.Our results demonstrate that NK cells from 3DL1+B*27 SPs can produce IFN-γ and TNF-α and express CD107a following K562 stimulation to a greater extent than those from 3DL1+Bw6.This finding is unlikely to be due to difference of VL as these 2 groups had a similar VL (Table 2).We have previously shown that NK cells from SP who carry *h/*y+B*57 have a level of trifunctional potential that is significantly higher than those from individuals carrying either 3DL1*h/*y or 3DL1*l/*x genotypes with Bw4 alleles other than B*27 or B*57.The elevated tri-functional potential of NK cells from *h/*y+B*57 carriers depends on the presence of both the 3DL1*h/*y receptor genotype and HLA-B*57 since carriers of 3DL1*l/*x with HLA-B*57 also have significantly lower NK tri-functional potential (Kamya et al. 2011).In contrast, we observed no differences in tri-functional potential in NK cells from HLA-B*27 positive SPs carrying either the 3DL1*h/*y or *l/*x receptor genotypes.It should be noted that a limitation in making this assertion is the small number of subject who were *h/*y+B*27 versus *l/*x+B*27 available to make this comparison.Epidemiological studies found that compared to Bw6 hmz the B*57 effect on time to AIDS and VL control was  (Martin et al. 2007).All but one of the 3DL1+B*27 group of subjects in our study population expressed B*27-80T alleles (Carrington, Martin, and van Bergen 2008).Furthermore, there is also evidence that B*2705 has a greater affinity for one or more of the KIR3DL1*l allotypes (Luque et al. 1996) (Kamya et al. 2011).There is also a trend towards NK cells from 3DL1+B*27 carriers having higher function that those from 3DL1+Bw4 individuals.These results argue in favour of HLA-B*27 and B*57 being unique among HLA-Bw4 antigens in their impact on educating NK cells for subsequent activity, although the effect of B*27 is more modest than that of B*57.According to the rheostat model of NK education, the strength of the inhibitory input received by NK cells determines the threshold of activation that is set in each NK cell.The higher the inhibitory input, the more likely the NK cell will pass the threshold required to respond to stimuli with an increased frequency of effector cells and an increased number of effector functions (Brodin, Karre, and Hoglund 2009).During development, NK cells must acquire sufficient inhibitory signals to prevent autoreactivity through recognition of ligands for inhibitory NK receptors (Valiante et al. 1997;Hoglund et al. 1997).The larger the contribution of given receptor-ligand pairing to NK cell inhibition under homeostatic conditions the more potent a missing self response will be when the ligand is lost.This situation would be encountered in a setting of HIV infection where HIV encoded Nef downmodulates HLA-A and B molecules from the cells surface abrogating inhibitory signals mediated by 3DL1 receptors (Collins et al. 1998;Cohen et al. 1999).
In this report we have focused on comparisons of the tri-functional subset of NK cells.This was done because the percent contribution of this subset to the entire K562 stimulated response was the only functional subset that differed between carriers 3DL1+B*27 and a KIR/HLA receptor-ligand combination unable to signal through 3DL1 NK receptors.NK cells able elicit 3 functions are more potent in terms of the intensity of each of their functions than corresponding mono-functional NK cells (Kamya et al. 2011).This is similar to what has been reported for poly-versus mono-functional CD8 + T cells (Darrah et al. 2007;Betts et al. 2006) Poly-functional HIV-specific CD8 + T cells in SPs may play a role in superior anti-HIV activity (Betts et al. 2006;Makedonas and Betts 2011).This is still a controversial area as the low VL seen in SPs may preserve multi-functional HIV-specific immune response.Although the biological relevance of poly-functional antigen specific CD8 + T cells in HIV infection is not yet clear, they do serve as an indicator of an effective response to HIV.Our experiments did not directly test the anti-viral activity of NK cells since we did not use HIV infected cells as stimuli.The role of tri-functional NK cells in inhibition of viral replication warrants further investigation.If stimulation with HIV infected cells produces higher functionality in NK cells from 3DL1+B*27 versus 3DL1+Bw6 carriers and tri-functional NK cells are endowed with a superior capacity to suppress viral replication it would be interesting to study the ability www.intechopen.comHIV Infection in the Era of Highly Active Antiretroviral Treatment and Some of Its Associated Complications 206 of NK cells from 3DL1+Bw6 for other NK cells functions.Our results demonstrate that these individuals have a limited NK cell tri-functional potential upon missing self stimulation.Since these SPs are able to control viral replication and/or maintain CD4 counts above 400 for 7 or more years it is not unreasonable to assume that NK cells from these subjects possess other NK function.NK cells are known to mediated antibodydependent cell-mediated cytotoxicity which has been shown to play a role in controlling viral replication (Forthal, Landucci, and Daar 2001) and may play a role in preventing infection (Rerks-Ngarm et al. 2009).In addition, NK cells are also able to regulate antiviral immunity by modulating DC function (Gerosa et al. 2002;O'Leary et al. 2006).In the presence of HIV replication the cross talk between NK cells and DC is impaired (Mavilio et al. 2006;Melki et al. 2010;Alter et al. 2010).It would be interesting to assess whether the interaction between NK cells and DC is maintained in SPs, particularly in 3DL1+Bw6 carriers.

Conclusion
We have demonstrated that NK cells from 3DL1+B*27 SPs have a higher tri-functional potential following K562 stimulation than those from 3DL1+Bw6.A test of trend found that NK tri-functional potential declines significantly in NK isolated from carriers of the following genotypes: *h/*y+B*57 > 3DL1+B*27 > 3DL1+Bw4.Our results suggest that although the protective effect on HIV infection conferred by HLA-B*27 is mediated in part by CD8 + T cells recognizing HIV epitopes restricted by this allele, the protective effect of this alleles may also be mediated by its interaction with inhibitory 3DL1 receptors.HLA-B*27, like HLA-B*57, appears to have an impact on NK education that is superior to that of other Bw4 alleles.Although this remains to be demonstrated experimentally we hypothesize that in carriers of certain 3DL1 and HLA-B*27 or HLA-B*57 genotypes, virusinfected cells that have down modulated the HLA ligand for their inhibitory 3DL1 NK receptors may be able to recruit a larger number NK cells with multiple functions, which can play a role in viral control.Such information is relevant to vaccine design by providing a rationale for modulating NK activity at the time of vaccination to favor developing protective immunity.

Fig. 1 .
Fig. 1.NK cells from individuals carrying the 3DL1+HLA B*27 NK receptor-ligand pair have an increased functional potential.The frequency of NK cells that secrete IFN-γ (left), express CD107a (middle) or secrete TNF-α (right) in 3DL1 hmz individuals who carry HLA-B*27 or HLA-Bw6.Each data point represents a separate individual.The bar through each scatter plot indicates the median frequency for the group.A Mann-Whitney U test was used to assess the significance of between-group comparisons (A).The percent contribution of seven different functional profiles to the total NK cell response to K562 HLA-devoid cells from individuals carrying 3DL1+B*27 (n=12) and 3DL1+Bw6 (n=14).Below the x-axis, dots refer to the presence of each functional marker (CD107a, IFN-γ and TNF-α) in that profile.The height of each bar represents the median for the group and the height of the error bar the interquartile range for that group.An asterisk (*) over the line linking two bars indicates that the contribution of that functional subset of the NK cell response was significantly different in the two study populations.A Mann-Whitney U test was used to assess the significance of between-group comparisons and p<0.05 was considered significant (B).

Fig. 2 .
Fig. 2. Comparisons of the tri-functional potential of NK cells from study subjects with defined KIR/HLA combinations.Scatter plots show percent contribution of tri-functional NK cells to the total K562 stimulated response in individuals who are 3DL1+B*27, 3DL1+Bw4 and 3DL1+Bw6 carriers (A), and *h/*y+B*27 and *l/*x+B*27 carriers (B).Each data point represents results from a separate individual.The data point represented by an empty square and triangle refer to individuals that carry both B*27 and B*57.The bar through each scatter plot indicates the median frequency for the group.A Mann-Whitney U test was used to assess the significance of between-group differences.
Fig. 3. Comparisons of the tri-functional potential of NK cells from individuals carrying 3DL1+B*27, *h/*y+HLA-B*57 and 3DL1+Bw4.Scatter plots show percent contribution of trifunctional NK cells to the total K562 stimulated response in individuals who are 3DL1+B*27 and *h/*y+B*57 carriers (A) or *h/*y+B*57, 3DL1+B*27 and 3DL1+Bw4 carriers (B).Each data point represents results from a separate individual.The bar through each scatter plot indicates the median frequency for the group.A Mann-Whitney U test was used to assess the significance of between-group differences (A).A Spearman's correlation test was used to assess the significance of a trend towards decreasing functional potential in carriers of these genotype combinations (B).

Natural
Killer Cells from HIV Infected Slow Progressors Who Carry the Protective HLA-B*27 Allele and Inhibitory KIR3DL1 Receptors Have Elevated... 205 enhanced in the presence of 3DL1*h/*y compared to 3DL1*l/*x.Overall, the effect of B*27 on these outcomes was more moderate than that of B*57 in the presence of 3DL1 *h/*y.Compared to Bw6 hmz the B*27-80T allele B*2705 was more protective in the presence of 3DL1*l/*x than in the presence of 3DL1*h/*y

Table 2
Natural Killer Cells from HIV Infected Slow Progressors Who Carry the Protective HLA-B*27 Allele and Inhibitory KIR3DL1 Receptors Have Elevated... www.intechopen.com

Table 2 .
Summary of study population characteristics.I In years, 2 Cells/mm 3 , 3 Means ± standard deviation.
(Boulet et al. 2010;Kamya et al. 2011)sults we concentrated on the tri-functional NK subset in subsequent analyses.We next compared the K562 stimulated NK cells from 3DL1+B*27 individuals to that from carriers of 3DL1+Bw4.NK cells from *h/*y+B*57 carriers have previously been shown to have superior tri-functional potential compared to 3DL1+Bw6 and *h/*y+Bw4 subjects(Boulet et al. 2010;Kamya et al. 2011).Since HLA-B*57 is a Bw4 allele we excluded carriers of either HLA-B*57 or HLA-B*27 alleles from the 3DL1+Bw4 group.
. Our findings that NK cells from *h/*y+B*27 and *l/*x+B*27 carriers have similar levels of trifunctional potential that may be more modest than of *h/*y+B*57 carriers is in line with B*27 being able to interact with receptors encoded by 3DL1*h/*y and *l/*x genotypes in 3DL1+B*27 carriers and this more effectively that B*57 interacting with receptors encoded by 3DL1*l/*x genotypes