1 Antibody Concentration – Primary and Secondary Response Primary Response 1.Infection (Ag) 2.Lag phase 3Antibodies produced 4Antibody level rises to combat infection 5Ag dealt with 6Ab level declines – short lived 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 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 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

4 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 – Phagocyte (has enzymes) Partial digestion of Ag Ag still whole Antigen presenting cell (antigen presentation)

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

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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 An antibody molecule 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 Constant region (Fc) Related to class of Ab Enables Ab to bind to receptors and attach to cells – e.g. Phagocytes / mast cells Produced by B lymphocytes Large globular proteins – Y shaped 4 polypeptide chains (held together by S-S (disulphide) bonds Hinge region – allows spatial flexibility to branches of the Y shaped variable region of the Ab Allows for binding to more than one Ag

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

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

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12 Communication between cells Cell Signalling in Immune Response

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