Question

Based on what you know about antigens and antibodies, what blood type is the universal donor? Explain.

Answer 1

ANTIGENS :

The molecular substances like polysaccharides ,proteins, lipoproteins, nucleoproteins, nucleic acids, etc., that can induce a detectable immune response are called antigens. They can be recognized by B cells or T cells (if presented by APCs or ASCs). the antigenic site that binds to a paratope of antibody is called the epitope. Based on their existence, they are of various types like free or circulatory antigens that freely circulate in the body fluids, intra cellular antigens which are present inside the infected cells and cell surface antigens such as blood group antigens.

PROCESSING AND PRESENTATION OF ANTIGENS :

whenever a pathogen enters the cells, it gets broken down by the action of enzymes released from lysosomes,.these broken pieces are called antigenic determines (epitopes). This is called the processing of antigens. These antigenic determinants are presented by specialised group of molecules called major histocompatability complex (MHC) molecules( called human leukocyte antigen /HLA System in human beings )which are of two types namely class 1and class 2 MHCs.

CLASS 1MHC MOLECULES : they are found on the surface of almost all nucleated cells of the body. They present the antigens to Tc cells for cell mediated immunity.

CLASS 2 MHC MOLECULES : They are found only on the surface of APCs( in addition to class 1 MHC molecules) And lymphocytes. They present the Antigens to TH called for cell mediated or humoral immunity.

ANTIBODIES :

Whenever pathogens enter our body, the B lymphocytes produce an army proteins called antibodies to fight against them. They are highly specialised for binding with specific antigens the part of an anti body that recognizes an antigen is called the paratope( Antigen binding site) .based on their mobility, antibodies are of two types, namely circulating or free antibodies and surface antibodies. The circulating or free antibodies are present in the body fluids where as the surface antibodies are present on the surface of the mature B cells as well as the memory cells.

STRUCTURE :

the basic structure of an antibody was proposed by RODNEY PORTER, is a Y shaped molecule with four polypeptide chains of which two are long, identical heavy chains( H) and two are small, identical light chains( L) .hence, an antibody is represented as H2 L2.The two chains are linked by sulphide bonds. One end of an antibody molecule is called Fan end (fragment antigen binding )and the other end is called Fc end (fragment - crystallizable or fragment -cell binding). Based on the structure, the antibodies are of five types namely IgD, IgE, IgG, IgA, IgM.

The blood group "O " is called universal donar ,because their donated red blood cells have no aA, B or The antigens and can therefore be safely given to people of any blood group.. Their plasma does not have A, B so doesn't react with other blood types like A, B, AB.

So they are called universal donars.