NK cells and KIRs: Structure and Functions

EFI-ASHI-APHIA Summer School 2013 Stintino

16 – 18 September 2013

Carlo Carcassi

Natural Killer cells (NK) •  About 10% of lymphocytes

(CD56+CD3-) •  Kill target cells

(e. g. leukemic blasts, infected cells)

•  Are regulated by specific receptors (e.g. KIRs)

•  Produce immunoregulatory cytokines (e.g. IFN-γ)

•  Regulate immune response

HLA class I molecules have a double function: - interact with NK cells in innate immune response and - with cytolytic T cells in adaptative immune response

HLA and KIRs

KIRs: what are they and where are they expressed?

They are a family of transmembrane glycoproteins

They are expressed on NK cells and a subset of T lymphocytes

What do they do?

They are key regulators of NK-cell development, tolerance and activation

Why are they so important?

Many studies have demonstrated a role for combinations of KIR receptors and their HLA Class I

ligands in a variety of diseases such as viral infections, autoimmune disorders and tumors.

Certain KIR-HLA combinations can influence pregnancy, hematopoietic stem cell transplantation

and also organ transplantation.

chr. 19q13.4

ILT

ILT

LAIR

KIR

FCaR

NK

p46

GPV

I

LRC

HLA class I and KIR: functionally related gene clusters exhibiting extreme polymorphism

chr. 6p21.3 MHC M

ICB

M

ICA

HLA

-B

HLA

-C

HLA

-J

HLA

-E

HLA

-A

HLA

-G

HLA

-F

HLA

-H

3DL3 2DL3 2DP1 2DL1 3DP1 Haplotype A

2DL4 2DS4 3DL2 3DL1

3DL3 2DS2 2DL2 2DL4 3DP1 2DL5 2DS1 3DL2 2DS5 3DS1 Haplotype B

KIR gene organisation

KIR gene organisation. The pseudoexon 3 and the deleted KIR3DP1 exon 2 is shown in red.

KIR gene organisation

The KIR gene products attain a high level of diversity

based upon four levels of variation:

(1) the product of each KIR gene specifically recognizes a

distinct subset of the available MHC-I allotypes

(2)

different combinations of the 14 KIR genes are

inherited as distinct haplotypes by individuals within

the human population, and different haplotypes can

vary in proportion of activating and inhibitory KIR

(3)

many distinct alleles of individual KIR genes have arisen

through point mutations encoding minor sequence

variations of one to several amino acids, which can

affect receptor surface expression level,

recognition by anti-KIR antibodies, and

affinity/avidity for MHC-I

(4)

diversity of the NK cell repertoire in peripheral

blood is generated through the stochastic

expression of different combinations of the

available KIR gene products on the surface of

individual NK cells

KIR Diversity •  Structural

•  Allelic

•  Haplotypic

•  Genotypic

KIR protein structures

KIR2DL4 is the unique long tail activating KIR, only expressed on CD56

high NK cells, stimulating a more potent activation of cytokine production

rather than cytotoxicity and associated with

FCεRI-γ adaptor instead of DAP12

http://www.ebi.ac.uk/ipd/kir/

Haplotypic diversity

KIR Nomenclature – Haplotype •  Basic set of 15 genes

•  2DL2 and 2DL3 behave as alleles

•  3DL1 and 3DS1 behave as alleles

KIR Nomenclature - Haplotype •  Each KIR haplotype has an official name:

KH-001 or KH-022B •  The A or B indicating whether the haplotype

belonged to the A or the B group •  Followed with a optional 17 digit binary code

indicating the presence or absence of each gene

•  KH-001-11100010011011011

Ligand unknown. Some alleles of 2DS4 have a 22bp deletion, the null allele has a population frequency of about 84% (allele frequency of 60%).

2DL4 may transmit inhibitory, stimulatory, or both types of signals. 2DL4 binds to HLA-G. Framework KIR gene

About 50% of the population espress only type A haplotypes -> inhibitory

Allelic variations of group A KIR haplotypes

KIR receptor ligands

2DL1 2DS1 HLA-Cwlys80

GROUP C2 (w2,4,5,6,707,1204,

15, 1602,17)

3DL1 3DS1 HLA-Bw4 3DL2 HLA-A3, -A11

2DL4 HLA-G

2DL2 2DL3 2DS2 HLA-Cwasn80

GROUP C1 (w1,3,7,8,12,13,14,

1507,1601)

KIR receptor ligands

KIR receptor ligands 2005

KIR receptor ligands

Molecular intervention, vol 5, issue 4 August 2005

1 KIR genotype

KIR Diversity

Molecular intervention, vol 5, issue 4 August 2005

Why? Homozygosis/heterozygosis?

Allelic polymorphism?

Promoter activity?

Only 45 % of HLA-A alleles are ligands recognized by KIRs Only 36 % of HLA-B alleles are ligands recognized by KIRs All HLA-C alleles present C1 o C2 epitopes.

Raja Rajalingam: Korean J Hematol 2011;46:216-28.

KIR HAPLOTYPES INHERITANCE

Raja Rajalingam: Korean J Hematol 2011;46:216-28.

KIR HAPLOTYPES INHERITANCE

NK cells thus make vital contributions to the immune system and the reproductive system. The former being essential for day-to-day survival of human individuals. The latter for the generation to generation survival of human populations and the human species