Antibody Concentration – Primary and Secondary Response

1. Primary Response • Infection (Ag) • Lag phase • 3 Antibodies produced • 4 Antibody level rises • to combat infection • 5 Ag dealt with • 6 Ab level declines – short lived Antibody Concentration – Primary and Secondary Response Secondary Response After the primary response, Ab’s do not stay in blood – the level declines If the body is infected by the same Ag a second time Ab’s must be made again Re-infection causes much more rapid and a stronger immune response – concentration of Ab’s rises sooner- reaches a higher concentration – more plasma cells than in 1o response – more cells to respond to Ag; less time to produce same number of plasma cells –hence, a greater [Ab] compared to 1o response; increased affinity of Ab for Ag. This is due to the presence of memory cells (made during the primary response) – no need for antigen presentation and clonal selection Long-lived; basis of vaccination

2. Primary – establishes immunological memory

3. Lag phase – antigen presentation (by macrophage /phagocyte); clonal selection (T + B lymphocytes); production of cytokines; B cell activation; clonal expansion; formation of plasma cells; protein (antibody synthesis B cells Humoral response Has Ag receptors – carries Ab (receptor) on surface Complimentary to only one Ag Clonal selection Each B cell – molecules of single type of Ab on outer surface of plasma membrane Selection and activation of appropriate B lymphocyte / B cell and T lymphocyte by APC’s (macrophages) Clonal expansion T cells divide by mitosis to form a clone (clonal expansion) - and secrete signal molecules termed cytokines (lymphokines) which stimulate the selected B cells to divide by mitosis to form a clone (clonal expansion) B cells specialise / differentiate to form larger Ab secreting plasma cells Ab’s are specific / complementary to Agnitiating the response B cells and T cells also differentiate into memory cells – long lived / remain in circulation – provide immunological memory to provide a secondary response on subsequent exposure to the same Ag; 2o response is more rapid and stronger; produces larger amount of Ab

4. Phagocyte (has enzymes) Partial digestion of Ag Ag still whole Antigen presenting cell (antigen presentation) Clonal selection – receptors On T cell membrane – complementary to Ag Clonal expansion (T cells) – divide by mitosis Clonal expansion (B cells) Remain in body to produce a rapid and stronger 2o response on exposure to the same Ag – divide to make Ab producing plasma cells –

5. Clonal Selection Ag selects B Cell with right Shape of recepror Clonal Expansion Divide by mitosis To form a clone of Plasma cells and a Clone of memory cells

7. B cell Smaller Origin – bone marrow + foetal liver cells Development – bone marrow + foetal liver Low nucleus to cytoplasm ratio – nucleus larger relative to cytoplasm Plasma cell Larger Derived from B cell Large nucleus to cytoplasm ratio – nucleus smaller relative to cytoplasm Develops extensive RER - increase in protein (antibody) synthesis; transport More ribosomes; more mitochondria (ATP for synthesis and secretion) More Golgi apparatus – for secretory vesicles;adding carbohydrate (to make glycoprteins) More space for organelles Ab (protein) made by ribosomes (RER); ATP required (mitochondria)

8. Ag binding site (Fab) Variable region – varies from one Ab to another – due to variable amino acid sequence (primary structure) – different 3o and 4o structures; different shapes antigen binding sites - ensures specificity for a particular Ag Specific shape – complementary to Ag – “Lock and Key” Bind with a specific Ag Produced by B lymphocytes Large globular proteins – Y shaped 4 polypeptide chains (held together by S-S (disulphide) bonds An antibody molecule Hinge region – allows spatial flexibility to branches of the Y shaped variable region of the Ab Allows for binding to more than one Ag Constant region (Fc) Related to class of Ab Enables Ab to bind to receptors and attach to cells – e.g. Phagocytes / mast cells

9. S-S (covalent) bonds hold polypeptide chains (H & L) together

10. Neutralisation and agglutination Mode of Action of Antibodies • also promotes phagocytosis by • the constant region attracting • phagocytes Immobilise pathogens (bind with flagellum) Destroy bacterial cell wall (lysis) Stop spread

12. Cell Signalling in Immune Response Communication between cells

13. Some Th cells become memory cells

14. Cell mediated immunity (CMI)

15. T cells Ag presentation by phagocytes Receptors on T cell surface complementary to Ag – specificity Clonal selection – Ag selects only those T cells with complementary receptors and activates them Clonal expansion - activated T cells divide by mitosis into a clone Th cells release cytokines (signalling chemicals) Stimulate B cells to divide by mitosis to form a clone of B lymphocytes (low nucleus to cytoplasm ratio) These differentiate into larger plasma cells (large nucleus to cytoplasm ratio) Secrete antibodies Tcyt – kill cells with intracellular parasites Tk – kill abnormal cells with markers for cancer Tsup – regulate immune response Memory T cells – able to differentiate rapidly into Th, Tcyt, Tk cells on stimulation with Ag a

16. Flow chart to represent the immune response