Kell blood group system

Kell blood group system most important blood group system following to ABO and Rh blood group system, particularly RhD as far as immunogenicity is concerned and Its clinical importance.

1. Kell Blood Group System Dr. RAFIQ AHMAD, MBBS/MD, MTM, FSAP

2. Introduction History Nomenclature Proteins/Genes and their functions Antigens Antibodies Clinical Significance

3. Kell -History First blood group antigen to be identified after the discovery of antiglobulin test ( Coomb’s test). KEL1 or K(Kelleher) identified in 1946 KEL2 or k( cellano ) identified in 1949 Kp a , Kp b and K null phenotype discovered in 1957 .

4. Nomenclature Number of Kell antigens: 35 ISBT symbol: KEL ISBT number: 006 Gene symbol: KEL Gene name: Kell blood group CD number CD238 In fetus Kell antigen appears very early during erythropoiesis , K – 10 -11 week old fetus, and k in 6 weeks old fetus

5. Kell Antigens Number: 35 The K antigen is one of the most clinically significant Kell antigens. Specificity: Protein: Amino acid sequence determines the specificity of Kell antigens

6. Kell Antigens Antigen-carrying molecules: Glycoprotein with enzymatic function The Kell glycoprotein is a transmembrane , single-pass protein that carries the Kell antigens. It is an endothelin-3-converting enzyme; it cleaves "big" endothelin-3 to produce an active form that is a potent vasoconstrictor

7. Kell Genetics Gene- Chromosome 7q33 Name KEL Organized into 19 exons of coding sequence Product Kell glycoprotein GENETICS: alleles K, k, Kpa , Kpb , Jsa , and Jsb are in " linkage disequilibrium "; no gene exists which carries both K and Kpa or Jsa , or both Kpa and Jsa . A. K/k, Kpa / Kpb and Jsa / Jsb inherited in autosomal , codominant fashion. McLeod syndrome is inherited in X-linked fashion .

8. Kell Genetics Molecular basis: The KEL gene encodes the Kell antigens.   KEL is highly polymorphic. It has two major codominant alleles, k and K, which result from a SNP (698C→T), and the corresponding k and K antigens differ by a single amino acid change (T193M).

9. Kell Frequencies ~100%:  k, Kp b , Ku, Js b , K11, K12, K13, K14, K18, K19, Km, K22, K26, K27 K antigen: 2%  in Blacks,  9%  in Caucasians, up to  25%  in Arabs ~2%:  Kp a , U1 a ~0.01%:  Js a   (0.01% in Caucasians, 20% in Blacks), Kp c , K23 Others: K17 (~0.3%), K24 (rare), VLAN (rare), K16 (unknown) K-k+  in 91% Caucasians and 98% Blacks ANTIGENIC STRUCTURE: Kell antigens located on red cell membrane glycoprotein(CD238) 4- 5 N- glycans present; no O glycosylation

10. Kell Antigens

11. Kell Antigen- Its Functions Kell glycoprotein is an endothelin-3-converting enzyme (big endothelins - ET3--  vasoconstriction) Kell glycoprotein is a memberof the Neprilysin (M13) sub-family of zinc endopeptidases and has sequence and structural homology with neutral endopeptidase ,( CALLA,enkephalinase ) and endothelin -converting enzyme ECE-1.

12. Kell structure – Xk Kell linked to Xk protein through a disulfide bond Xk –integral membrane protein which expresses the Kx blood group antigen(XK1) . XK gene encoding Kx antigen is located on X chromosome at Xp21.1 ,as a separate blood group system

13. Onset of expression of the components of the Kell blood group complex Expression of both Kell and XK is limited to the erythroid lineage,expression of Kell , but not of XK, was noted in bipotent erythroid - megakaryocyte progenitors. Thus the expression of Kell and XK is independent, and this is in keeping with previous studies, with transfected cells, that showed that coexpression of Kell and XK is not necessary for transport of the proteins to the cell surface - Jeffrey et al ., TRANSFUSION,2005

14. Phenotype Caucasians Percentage African- American Percentage RBB Dammam k 91 98 90% K+k + 8.8 2 9.1% K 0.2 RARE 0.9% Kp a RARE 0.1% Kp b 97.7 100 100% Kp ( a+b +) 2.3 RARE - Kp c 0.32 - Js( a+b -) 1 - Js(a-b+) 100 80 -

15. Kell Antigens KELL 1(K): low incidence antigen, 9% whites .3.5% in blacks . KELL 2(k): High incidence antigen in all populations This polymorphism arises due to SNP in exon 6, Met193Thr

16. KELL antigens Kp a (KEL3): 2%whites NOT IN BLACKS Kp b ( KEL4):It is the common allele, the codon is CGG. Kp a / Kp b / Kp c differ from the common allele by single base change in the same codon in exon 8, TGG and CAG respectively. Js a (KEL6): confined to African ethnicity 16% prevalence

17. Other KELL antigens Low prevalence antigens: Ul a , K23, KYO(single amino acid substitution) High prevalence antigens : k, Kp b ,Js b , K11,K14 OTHER HIGH INCIDENCE ANTIGEN: K12, K13, K18,K19,K22,TOU, RAZ,KALT, KTIM

18. Kx antigen Expressed most strongly on red cells that lack Kell antigens, ie ., K0 red cells Only antigen in Kx system X linked recessive gene Xk at Xp21 BLOOD GROUP SYSTEM:019 A part of dimeric amino acid transporter, covalent linkage to type 2 membrane Kell glycoprotein

19. K null (K ) and K mod phenotypes K : No kell antigens detectable in RBC Immunised individuals produce anti-Ku (anti-KEL5) Anti Ku – recognises universal Kell antigen (Ku)on all cells, except K Might be by nonsense/ missense /splice site mutations It has single specificity , can cause both HDFN and hemolytic reactions

20. K mod phenotype K mod is an inherited rare RBC phenotype characterized by weak but detectable expressionof high-incidence Kell antigens Homozygous or heterozygous for missense mutations in kell glycoprotein Some produce anti Ku,but nonreactive with K mod cells

21. Mcleod phenotype- serology They can make 2 alloantibodies after transfusion– anti KL , mixture of anti Kx and anti Km. Km antigen is found in all red cells other than K red cells / Mcleod phenotype .

22. LyonizationI -McLeod phenotype Mixed populations of Kx + and Kx – red cells, or of red cells with strong and weak Kell antigen expression are recognized in many female carriers of genes responsible for the McLeod phenotype . The proportion of McLeod phenotype red cells in female McLeod carriers usually varies from 5% to 85% . This dual population is often difficult to detect serologically, especially if Kell antibodies and not anti- Kx are used, but flow cytometry permits an accurate estimationof the two red cell populations

23. McLeod phenotype All Kell antigens are depressed , Xk absent on red cells Deletion of that part of the chromosome containing Xk Minority of X linked CGD have this phenotype includes the deletion of locus for a X linked GD and Xk locus Clinical features :

24. Mcleod Syndrome Clinical features: Acanthocytic red cells, elevated CK , Other muscular and neurological defects.

25. Weak expression of Kell antigens Other inherited causes for weak expression of kell phenotype when glycophorin C and D are absent (Leach phenotype); when a portion of the extracellular domain of glycophorin Cand D, specifically exon 3, is deleted (some Gerbich negative phenotypes). Acquired causes: AIHA, ITP, microbial infection

26. Tissue expression Kell protein detected in testis ,skeletal muscle, lymphoid tissues Not found in WBCs or platelets

27. Action of Enzymes on Kell Antigens Papain Ficin Resistant Trypsin Alpha chymotripsin 2ME/ DTT/ AET Mixture of trypsin Sensitive and chymotrypsin

28. Effect of Enzymes Enhanced antibody activity: Cleavage of glycoprotein leads to: Decreased activity : Cleavage of glycoprotein leads to 1.Reduces the negative charge on RBC 2.Reduces the steric hindrance 3.Making cells more hydrophobic It is seen in Rh , Kidd, P, lewis , I antigens loss of antigens , it is seen in Fy a , Fy b , MNS systems

29. Kell Antibodies-Anti- K Anti K and anti k Usually IgG ( IgG1) Causes severe HDFN and HTR Anti K -the most common immune red cell antibody other than ABO/ Rh system Most anti K appears due to blood transfusion, few are due to microbial infection ,few in healthy donors K is less immunogenic than D

30. Kell antibodies Anti K found in 1/1000 pregnant women Incidence of HDFN due to anti K -1/20000 pregnancies The frequency of HDFN due to anti K is lower as the mother is immunised by transfusion not by pregnancy In most cases fetus is K negative HDN due to anti K severe when immunization is due to previous pregnancy

31. K-HDFN Pathogenesis Kell glycoprotein appears earlier in erythropoiesis than D antigens Anti K induced phagocytosis of K+ erythroid progenitors FEATURES: Lower levels of reticulocytes /AF bilirubin / erythroblasts Less severe post natal hyperbilirubinemia Treatment : recombinant erythropoietin

32. K-HDFN Management T here is no correlation between antibody titer and degree of inhibition Neonates with Kell HDFN require less phototherapy and exchange transfusions . Because of the destruction of red cell precursor cells as well, treatment with erythropoietin may be more effective in neonates with Kell HDFN compared to Rh HDFN

33. Other antibodies Anti k cause severe hemolytic reactions, but less common Anti Kp b is an auto antibody in AIHA anti Js a ,anti Js b are rare, causing DHTRs Anti Ku in K individuals, reacts with all samples except K

34. The End!! Thank you