Antibody
Definition
An antibody (immunoglobulin) is a Y-shaped protein produced by B cells of the immune system in response to foreign substances (antigens). Antibodies specifically recognize and bind to antigens, marking them for destruction by other immune cells. There are five classes: IgG, IgA, IgM, IgE, and IgD.
Key Points for NEET
- 1Y-shaped protein with two heavy and two light chains
- 2Variable region binds specific antigen
- 3Five classes: IgG (most common), IgA, IgM, IgE, IgD
- 4Part of humoral (antibody-mediated) immunity
- 5Produced by plasma cells (differentiated B cells)
Example
IgE antibodies triggering allergic reactions when exposed to pollen
Asked in NEET
Common Mistakes to Avoid
- ✗Confusing antibody (produced by body) with antigen (foreign substance that triggers immune response)
- ✗Mixing up humoral immunity (antibodies from B cells) with cell-mediated immunity (T cells)
- ✗Thinking IgM is the most abundant — IgG is most abundant in blood; IgM is first to appear in primary response
Quick Revision Notes
- ⚡Y-shape: 2 heavy chains + 2 light chains; variable region (antigen binding) + constant region (effector function)
- ⚡IgG: most abundant, crosses placenta; IgA: in secretions (milk, saliva); IgE: allergies; IgM: first responder (pentamer)
- ⚡Primary response: slow, low antibody (mainly IgM); Secondary response: fast, high antibody (mainly IgG)
- ⚡Monoclonal antibodies: produced from single B-cell clone; used in diagnostics and cancer treatment
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