Antibodies are special plasma globulins having the feature of entering into the combination with the corresponding antibodies and creating the "antigen-antibody" complexes.
All types of antibodies are jointly called immunoglobulins. There are five classes of immunoglobulins IgG, IgA, IgM, IgE, IgD.
Antibodies to red blood cell antigens are immunoglobulins of M, G and A classes.
Scheme of "ANTIGEN-ANTIBODY" complex creation
Antibody heterogeneity directed against one antigen X
Schematic structure of immunoglobulins
IgG molecule has two active centers to be connected with the antigen. IgM molecule has ten active centers to be connected with the antigen, that's why IgM immunoglobulins enter into the reaction with erythrocytes easier than with IgG.
Reaction of erythrocyte direct agglutination by IgM antibodies and indirect agglutination by IgG antibodies
Reaction with anti-IgG is marked with green color - the Coombs test
Availability and absence of erythrocyte agglutination when adding reagents