T and B lymphocyte

What percentage of lymphocytes are B cells?

About 10% of peripheral lymphocytes.

What do B lymphocytes differentiate into?

Plasma cells that produce antibodies.

What are the major immunoglobulin classes and their key features?

• IgG: 75% of antibodies; crosses placenta; activates complement; long-term immunity.

• IgM: Pentamer; first antibody in primary response; strong complement activation.

• IgA: Dimer; protects mucosal surfaces; found in secretions (saliva, tears, milk).

• IgD: On B-cell surface; involved in B-cell activation.

• IgE: Mediates type I hypersensitivity; binds mast cells/basophils to trigger degranulation.

What percentage of lymphocytes are T cells?

About 80%.

Where are T lymphocytes mainly located?

Interfollicular areas of lymph nodes,

periarteriolar sheaths of spleen,

and thymus.

What are the main subsets of T lymphocytes and their roles?

• CD4 (Helper): Activate T, B, and macrophages.

• Regulatory (Treg): Suppress immune responses.

• CD8 (Cytotoxic/Killer): Destroy virus-infected or tumor cells via perforins and granzymes (ADCC).

What proportion of lymphocytes are NK cells?

Around 10%.

What is the main function of NK cells?

Destroy cells lacking MHC I (virus-infected or tumor cells) via perforins and granzymes; secrete IFN-γ.