(a) Define Humoral immune response. [1]
(b) Name any two types of antibodies found to give humoral immune response in humans. [1]
(a) Define Humoral immune response. [1]
(b) Name any two types of antibodies found to give humoral immune response in humans. [1]
(a) Humoral immune response:
The type of immunity in which B-lymphocytes produce antibodies that circulate in the body fluids (blood, lymph) and defend the body against antigens. It is also called antibody-mediated immunity (AMIS) because it is carried out by antibodies present in the 'humors' (body fluids).
(b) Two types of antibodies (any two):
- IgG
- IgA
- IgM
- IgE
- IgD
(Naming any two, e.g. IgG and IgM, earns the mark.)
Marking Scheme
- 11 mark (a): defining humoral response as antibody-mediated immunity by B-lymphocytes acting through body fluids (antibody-mediated / AMIS).
- 21 mark (b): naming any two antibody classes correctly (IgG, IgA, IgM, IgE, IgD) — ½ mark each.
Hint
Humoral = antibodies in body fluids from B-cells; the antibody classes all start with 'Ig'.
Quick Oral Answer
The humoral immune response is antibody-mediated immunity in which B-lymphocytes and plasma cells release antibodies into the body fluids to fight antigens; two antibody types active in humans are IgG and IgM.
Analysis & Explanation
Concept — Two arms of specific immunity:
Acquired (specific) immunity has two components:
- Humoral immune response (AMIS): mediated by antibodies secreted by B-cells / plasma cells, acting in body fluids.
- Cell-mediated immune response (CMI): mediated by T-lymphocytes, which act against infected cells, grafts, etc.
Why it is called 'humoral':
The term comes from 'humors', the old word for body fluids, because the antibodies float freely in blood and lymph rather than being fixed to cells.
Antibody structure link:
Each antibody is a protein with four peptide chains (two heavy + two light), written as , and the human classes are IgA, IgD, IgE, IgG and IgM.
Exam trap:
- Do not write T-cell responses here — antibodies come from B-cells.
- The question asks for types of antibodies (Ig classes), not the parts of an antibody. Writing 'heavy and light chains' will not score.
Common Mistakes
- 1Attributing the humoral response to T-lymphocytes; it is mediated by antibodies from B-cells (T-cells drive cell-mediated immunity).
- 2Listing antibody chains (heavy/light) instead of antibody classes (IgG, IgA, IgM, IgE, IgD) as asked in part (b).
- 3Writing vague definitions like 'immunity by blood' without mentioning antibodies or B-cells.
Interesting Facts
The five human antibody classes are IgA, IgD, IgE, IgG and IgM; IgG can cross the placenta to give a newborn passive natural immunity.
IgA is secreted in colostrum, the first milk, giving breastfed infants passive protection against gut infections.
Each antibody molecule is Y-shaped with two identical antigen-binding sites, allowing it to neutralise or tag antigens for destruction.
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Frequently Asked Questions
What is the difference between humoral and cell-mediated immunity?
Humoral immunity is carried out by antibodies produced by B-lymphocytes that act in body fluids against free antigens, while cell-mediated immunity is carried out by T-lymphocytes that act directly against infected cells, tumour cells and grafts.
How many types of antibodies are there in humans?
There are five classes of antibodies (immunoglobulins) in humans: IgA, IgD, IgE, IgG and IgM. Any two of these are acceptable for the second part of the question.