ABH antigens

A, B and H antigens on red cells are predominantly glyco-proteins, the majority being on the N-glycans of the anion exchanger (band 3) and the glucose transporter. ABH antigens on red cells are also expressed on glycosphingolipids, which include paraglobosides (Table 15.6). Soluble ABH antigens are

Table 15.6 Some glycolipids of the red cell surface expressing H, A, B, P1, PK, P and LKE activity.

Structure

Antigen

Name

Paragloboside series

Galß l ^4GlcNAcß l ^3Galß l ^4Glc-Cer Fuca l ^2Galß l ^4GlcNAcß l ^3Galß l ^4Glc-Cer Fuca l ^2Galß l ^4GlcNAcß l ^3Galß l ^4Glc-Cer 3 t l

GalNAc

Fuca l ^2Galß l ^4GlcNAcß l ^3Galß l ^4Glc-Cer 3 t l

Type 2 H Type 2 A

Type 2 B

Paragloboside

Globoside series

Galßl^4Glc-Cer Galal^4Galßl^4Glc-Cer GalNAcß l ^3Galal ^4Galß l ^4Glc-Cer NeuAca2^3Galßl^3GalNAcßl^3Galal^4Galßl^4Glc-Cer Fucal^2Galßl^3GalNAcßl^3Galal^4Galßl^4Glc-Cer

Type 4 H

Lactosylceramide, Gb2 Globotriosylceramide, Gb3 Globoside, Gb4 Sialosylgalactosylgloboside Globo-H

Cer, ceramide; Fuc, fucose; Gal, galactose; GalNAc, N-acetylgalactosamine; Glc, glucose; GlcNAc, N-acetylglucosamine.

glycoproteins. Differences in the terminal sugars of the glycoproteins and glycolipids determine the specificity of these antigens: L-fucose (Fuc) for H; L-fucose + N-acetyl-D-galactosamine (GalNAc) for A; and L-fucose + D-galactose (Gal) for B.

Two major types of carbohydrate chain endings serve as acceptors for the fucosyltransferases that synthesize H antigen. Type 1 and type 2 chains have Gal joined to N-acetylglu-cosamine (GlcNAc) through 1^3 and 1^4 linkages respectively. A- and B-transferases synthesize the transfer of Ga1NAc and Gal, respectively, from their donor substrates UDP-GalNAc and UDP-Gal, to the terminal galactosyl residue of type IH and type 2H, creating A and B epitopes and masking H specificity (Figure 15.1).

Secretory glycoproteins possess both type 1 and type 2 linkages, whereas red cells synthesize type 2 chains only. Plasma glycolipids, passively adsorbed onto the red cells have only type 1 chains; these also carry Lewis antigens (see p. 231). Other chains, called type 3 and 4, are also present in low numbers on

FUT1 or FUT2

H-transferase (a1,2-fucosyltransferase) ' O

A-transferase (GalNAc-transferase)

GalNAc

B-transferase (Gal-transferase)

No product

Figure 15.1 Biosynthetic pathway of H antigen from its precursor, and of A and B antigens from H. H remains unconverted in the absence of A or B gene products. R, remainder of molecule.

red cells, but probably only on glycolipids. Type 3, 4 and 6 chains are found in heart and kidney tissues, and may be target epitopes for the rejection of transplanted organs.

Was this article helpful?

0 0
How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book


Post a comment