COMPONENTS OF ADAPTIVE IMMUNITY Flashcards
Immune Response definition, dependency and outcome.
Definition: Reaction to and interaction with substances identified as non-self.
Depends on: A functioning thymus and conversion of stem cells into B and T cells.
Outcome: Antibody production, cellular immunity, immunologic memory.
Components of Adaptive Immunity
π‘οΈ Type: Acquired specific immunity (third-line defense).
βοΈ Consists of:
1οΈβ£ T cell lymphocytes
2οΈβ£ B cell lymphocytes
3οΈβ£ Antibodies
Lymphocytes
π Definition: Smallest leukocytes, circulate in blood/lymph, migrate into tissues.
π― Function: Provide immune defense against specific targets.
π Types:
B cells
T cells
Natural Killer (NK) cells
B Cells
π¦ Discovery: First identified in the bursa of Fabricius (birds).
𦴠Maturation Site: Bone marrow.
π‘οΈ Function:
Produce antibodies.
Circulate in blood.
Responsible for antibody-mediated (humoral) immunity.
T Cells
π Maturation Site: Thymus.
π οΈ Types:
1οΈβ£ T Helper (TH) cells
2οΈβ£ T Cytotoxic/Killer (TC) cells
β‘ Function: Directly destroy specific target cells via cell-mediated immunity (releasing chemicals that punch holes in target cells).
B & T Cell Differentiation
π± NaΓ―ve Lymphocytes: Have not encountered an antigen.
β‘ Effector Lymphocytes: Activated lymphocytes that have differentiated.
π Memory Cells: Some activated B/T cells differentiate into memory cells.
π§ͺ Plasma Cells: Activated B cells that secrete antibodies and present antigens to T cells.
Types of Activated T Cells
πͺ Cytotoxic T Cells (TC): Kill infected cells.
π οΈ Helper T Cells (TH): Help activate B cells and other immune cells.
π Regulatory T Cells (Treg): Suppress immune response when antigen is gone.
B-Cell Receptor (BCR)
βοΈ Structure:
Membrane immunoglobulin (IgM/IgD) + disulfide-linked IgΞ±/IgΞ² heterodimers.
π¬ Function: Recognizes free antigens.
π Signaling: IgΞ±/IgΞ² molecules required for signal transduction.
π― Recognition Sites: Two identical antigen-binding sites.
T-Cell Receptor (TCR)
π Function: Recognizes peptide-MHC complexes on antigen-presenting cells (APCs).
βοΈ Structure:
TCR for recognition
CD3 & zeta chain for signal transmission
π― Recognition Sites: One antigen-binding site.
T Cell Surface Proteins (CD Markers)
πΉ CD4: Found on Helper T cells & Regulatory T cells.
πΈ CD8: Found on Cytotoxic T cells.
β‘ Functions:
Signal transduction.
Promotes adhesion between T cells & APCs.
Two Arms of Adaptive Immunity
1οΈβ£ Antibody-mediated (Humoral) Immunity
2οΈβ£ Cell-mediated Immunity
1) Antibody-Mediated (Humoral) Immunity
π§ͺ Definition: Antibody production in response to antigens.
π Process:
NaΓ―ve B cellβs Ig binds to antigen β B cell proliferates β Becomes lymphoblast β Differentiates into plasma cells & memory cells.
π‘οΈ Targets:
Extracellular bacteria
Bacterial toxins
Viruses (before entering host cells)
π Defense Mechanism:
Binds to antigens/opsonized antigens β Forms immune complexes.
2) Cell-Mediated Immunity
π¬ Definition: Involves activated T cells to detect & eliminate intracellular microbes or tumor cells.
β οΈ Also involved in: Transplant rejection.
π― Targets:
π¬ Microbes inside phagocytes:
Intracellular bacteria (Mycobacteria, Listeria, Legionella).
Fungi (Cryptococcus).
Protozoa (Leishmania, Trypanosoma).
π¦ Microbes in non-phagocytic cells:
Viruses
Protozoa (Plasmodium, Cryptosporidium).
Antibody (Immunoglobulin, Ig)
π§ͺ Definition: Proteins secreted by plasma cells in response to antigens.
π― Function: Bind specifically to antigens.
π οΈ Structure:
Y-shaped molecule.
Arm region: Binds antigen.
Tail region: Determines function after antigen binding.
Antibody Structure
π Composition:
4 peptide chains:
2 light (L) chains
2 heavy (H) chains
Disulfide bonds:
Inter-chain links H & L chains.
Intra-chain bonds within each
polypeptide.
π οΈ Regions:
Variable region (V) - antigen specificity.
Constant region (C) - functional properties.
π Hinge region: Provides flexibility.
𧬠Glycoprotein: Carbohydrates attached to C region.
Antibody Classes & Functions: IgG
π‘ IgG (Most abundant, 75%)
Versatile (can perform all Ig functions).
Main antibody in secondary immune response.
Crosses placenta (except IgG2).
Fixes complement (except IgG4).
Good opsonin (enhances phagocytosis).
Antibody Classes & Functions: IgA
π‘ IgA (2nd most abundant)
Monomer in serum, dimer in secretions.
Major Ig in secretions (tears, saliva, mucus).
Important for mucosal immunity.
Antibody Classes & Functions: IgM
π‘ IgM (First Ig produced)
Pentameric structure (linked by J chain).
First Ig made by fetus & naΓ―ve B cells.
Good complement activator & agglutination agent.
Antibody Classes & Functions: IgD
π‘ IgD (Least understood)
Monomeric.
Low serum levels.
Primarily functions as a B-cell receptor.
Antibody Classes & Functions: IgE
π‘ IgE (Allergy & parasite defense)
Monomeric.
Binds tightly to mast cells & basophils β Triggers allergic reactions.
Involved in parasitic infections (binds to eosinophils for helminth defense).
