Humoral Immunity Provided By

Humoral immunity is provided by:

Correct Answer: B-lymphocytes

Humoral immunity (antibody-mediated immunity) is provided by B-lymphocytes, which differentiate into plasma cells upon antigenic stimulation and secrete antibodies (immunoglobulins).

Types of Adaptive Immunity

• Humoral immunity (B-lymphocytes): Mediated by antibodies in body fluids (blood, lymph, secretions). Effective against extracellular bacteria, viruses, and toxins.
• Cell-mediated immunity (T-lymphocytes): Mediated by cytotoxic T cells (CD8+) and T-helper cells (CD4+). Effective against intracellular pathogens (viruses, intracellular bacteria, fungi) and cancer cells.

Role of T-helper Cells

• T-helper cells (CD4+ T cells) are crucial for activating B-lymphocytes — they do not directly produce antibodies but are essential co-stimulators of humoral immunity.
• In HIV/AIDS, destruction of T-helper cells (CD4+ cells) impairs both humoral and cell-mediated immunity.

Immunoglobulin Classes (produced by B cells/plasma cells)

• IgG: Most abundant; crosses placenta; secondary immune response.
• IgM: First antibody produced in primary response; pentameric structure.
• IgA: Secretory antibody in colostrum, saliva, tears, mucosa.
• IgE: Mediates allergic reactions; involved in anti-parasitic defense.
• IgD: B-cell surface receptor; function less well understood.