[Biology Class Notes] on MNS Blood Group System Pdf for EXAM

As we know, blood is one of the most important parts of the human body. It is the medium through which different body systems operate smoothly as it provides the required amount of nutrients and oxygen. It is also a medium to transport the waste materials from the body and maintain body mechanisms. However, plasma is the major constituent of blood. Apart from that, several other things like RBC, WBC, and platelets are the sole constituents of the blood.

But depending upon the tiny substances present on the red blood cells MNS blood group system is derived. Tiny substances like M, N, S are known as antigens. The advanced genetic and anthropological studies of the human population revealed the presence of more than 40 antigens in the MN blood group. Initially, in the year 1927, the scientists located only two antigens, such as M and N and known as the MN Blood group. Later after 20 yrs another two antigens, S and s added to the list in the years 1947 and 51.

MNSs Blood Group Nomenclature:

Normally a protein consists of sugar attached to the MNSs called glycophorin. The blood group of the person is determined from the protein that attaches to the cell. The MNSs blood group is mainly denoted by two genes such as GYPA AND GYPB, containing glycoprotein A and Glycoprotein B. Another protein is also adjacent to glycoprotein B, which is CYPBthe allele for the MNS Blood group. The antigens in response produce antibodies; the antibodies of m and n don’t show any incompatibility reaction. However, the antibodies of s and s show transfusion reaction and can cause erythroblastosis fetalis. 

Usually, five common phenotypes are observed. Three most common phenotypes include M+n+s+s (24%) , M+N+ s+ s (22%)  and M+ n+ s+s (15%) . Two other phenotypes were also observed, having a frequency of 33% and 19%.

Apart from this, some other phenotypes were also observed because of mutation with GYPA and GYPB. Example- GYPA allele produces Mta antigen by single nucleotide polymorphism, and that results in a change in amino acid threonine to isoleucine.

Sometimes we also observe rare blood groups such as En – ve because of the lack of glycophorin in the RBC membrane. This is the primary reason for the mutation. Deletion or erection of additional gene results In the formation of the mutants. Such rare blood groups like S-s-U are formed. Individuals having this unique blood group lack both glycophorin A and B. After deep microscopic observation, it is noticed that MNSs antigens are mainly found in RBC. Glycophorin A mainly forms around 1 million copies, whereas glycophorin B forms around 0.2 million copies. The antigenic character of the MN blood group was also noticed in the kidney.

The Function of MNS Antigen:

The two major proteins in the RBC, Glycophorin A, and B, act as a carrier for the receptor of cytokines, bacteria, and viruses. But the organism that lacks the glycophorin sufferer from the disease as their function is not significant. The advancement in the field of medical science allows scientists to analyze deeply. Recently it has been noticed that scientists are taking their interest in glycophorin because it forms MN antigen. This glycophorin may be the receptor of plasmodium falciparum, the causal organism of malaria in humans. So technically, the persons having rare blood groups are resistant to plasmodium.

Molecular Data of MN Blood Group

GYPA and GYPB are the two primary proteins that are responsible for the encoding of the glycophorins in the MN blood group. Both the chromosomes show recombination reactions and are tightly linked. One can find both GYPA and GYPB in the long arm of chromosome 4.

Another gene present adjacent to the GYPB is GYPE. It is the gene that forms new alleles. Both the genes GYPA and GYPB contribute about 97% of the total homologous sequence. It also undergoes a duplication reaction.

The gene GYPA contains seven exons and having two forms of the allele, such as MNS 1 and MNS 2. These two alleles mainly produce two antigens, such as M and N. The two alleles are similar but from different amino acids such as serine at residue-1 and glycine at residue -5. GYPB has mainly five exons and having two alleles MNS3 and MNS4. It produces antigen S and s. Proteins like Methionine form at residue-29 and threonine at MNS4.

Glycophorin A and B are transmembrane proteins. At the negative charge surface of the RBC membrane, this Glycophorin A attaches and produces sialic acid. It has mainly three domains such as extracellular domain, intracellular domain, and spinning domain. The structure of Glycophorin B is similar to that of Glycophorin A, but the intracellular domains are shorter.