Which immunoglobulin isotype is the first produced during a primary immune response?

Which immunoglobulin isotype is the first produced during a primary immune response?

• A. IgA
• B. IgM
• C. IgG
• D. IgE

Answer: (B)

In a primary immune response, the initial antibody response comes from naive B cells that express membrane-bound IgM (and IgD) on their surface. Upon encountering antigen with help from T cells, these B cells differentiate into plasma cells that first secrete soluble IgM. IgM is a pentamer, which gives it high overall avidity and makes it particularly effective at activating the classical complement pathway early in infection. As the response matures, B cells undergo class-switch recombination, guided by cytokines, to produce other isotypes such as IgG, IgA, or IgE. So IgM is the first isotype produced in a primary response, with other isotypes appearing later after further maturation and memory formation.

In a primary immune response, the initial antibody response comes from naive B cells that express membrane-bound IgM (and IgD) on their surface. Upon encountering antigen with help from T cells, these B cells differentiate into plasma cells that first secrete soluble IgM. IgM is a pentamer, which gives it high overall avidity and makes it particularly effective at activating the classical complement pathway early in infection. As the response matures, B cells undergo class-switch recombination, guided by cytokines, to produce other isotypes such as IgG, IgA, or IgE. So IgM is the first isotype produced in a primary response, with other isotypes appearing later after further maturation and memory formation.