Final answer:
Cold agglutinins are IgM antibodies that cause the clumping of red blood cells, with IgM being highly efficient at agglutination due to its structure. Agglutination tests can be used to detect the presence of specific IgM antibodies or antigens in patient serum.
Step-by-step explanation:
The student is asking about the type of immunoglobulin that is responsible for cold agglutinins. Cold agglutinins are typically IgM antibodies. These antibodies can cause agglutination, or clumping, of red blood cells at low temperatures. Agglutination is a reaction where antibodies link pathogens together into larger aggregates. IgM, with its pentameric structure, provides ten Fab binding sites per molecule, making it very efficient at agglutination compared to other immunoglobulin classes like IgG.
In practical applications, a positive agglutination test for antibodies like the rheumatoid factor (RF) uses IgM antibodies. Latex beads coated with antigen will show positive agglutination when the serum contains the specific IgM antibodies against the antigen. Conversely, a positive agglutination test for antigens is observed when latex beads coated with antibodies agglutinate in the presence of serum containing specific antigens.