Chapter 6 Adaptive Immunity “third line of defense” Develops more slowly Specific Memory.
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Chapter 6
Adaptive Immunity
“third line of defense”
Develops more slowly
SpecificMemory
Adaptive Immunity
Antigens – “foreign or non self” (Ag= foreign proteins)◦ Viruses, bacteria, cancer, fungi or parasites◦ Noninfectious – pollens, foods, bee venoms◦ Drugs, vaccines, transfusions and
transplants
Adaptive ImmunityPrincipal cells: Lymphocytes
◦Accessory cells: APC & dendritic cells◦Effector cells
B cells → antibodies to blood → Ag T cells → attack Ag directly
Functionally◦ Regulatory◦ Effector
Specific◦ Each cell recognizes only ONE specific Ag
25-35% of blood leukocytes 99% reside in the lymph glands 60-70% of blood lymphocytes are T-cells
and 10-20% are B-cells
Foreign protein recognition:”surface receptor proteins-unique”◦ B-cells: membrane bound immunoglobulin◦ T-cells: self-recognition protein(major
histocompatibility complex)
“self from non self” Chromosome # 6 Two Classes
Class I *: endogenous pathogens -viruses & cancer Cytotoxic T cells… “must destroy me”
◦Class II : extracellular pathogens - bacteria & toxins Phagocytic cells: macrophages, dendritic cells, B
lymphocytes : Ag binds with MHC II Helper T
cell (CD4+) Human Leukocyte Antigens:WBCs
◦ Multiple allelles: A (120 genes) & B (250 genes)◦ Halotype: inherited unit
* all nucleated cells… not on RBCs
Class I… “all nucleated cells” (endogenous antigens)*
Function:present processed antigen to cytotoxic CD8+ T cells or
NK cells
“constant screening”
* Seen as abnormal…autoimmune disease
Class II …APC (dendritic, B cells, macrophage)
(exogenous antigens)
Function: presents processed antigen fragment to CD4+ T cells
effective interaction among immune cells*
*Figure:6-1
“Additional membrane bound proteins” Uses
◦ Aid the function of the immune cells◦ Define the functionally distinct subset of cells
CD4+ helper T cells – binding receptor: from APCs
CD8+ cytotoxic T cells- binding receptor: from all nucleated cells
Adaptive Immunity
Clonal diversity – 1st phase – fetus
◦ Recognition of millions* of foreign Ag◦ Large population of T & B cells◦ Develop in primary lymphoid organ (thymus,
bone marrow)◦ Migrate to secondary lymphoid organs
*108 or 100 million foreign antigens(proteins)
Generation of Clonal Diversity“primary lymphoid organ – fetus”
Lymphoid stem cell B and T cells recognize more than 108
antigens B lymphocytes – bone marrow “hormones”
– to secondary lymphoid organs* T lymphocytes – thymus “hormones” to
second lymphoid organs*
*lymph nodes & spleen
Secretory (Mucosal) Immune System
Lymphoid tissue that protects the external surface of the body
Ab present in tears, sweat, saliva, mucus and breast milk.
IgA dominant immunoglobulin◦ Prevent attachment and invasion of
pathogens
Adaptive Immunity“two arms”Humoral – B cells
◦ Antibodies – bacteria, viruses, and toxinsCell mediated – T cells
◦ Subpopulations React directly with Ag on cell surfaces –
NK(see next slide) Stimulate other leukocytes (cell to cell or
cytokines) T Cytotoxic cells – viruses infected cells and cancer
“lymphocytes” :functionally & phenotypically distinct from T cells, B cells, and monocyte-macrophages
◦ Automatically kill foreign cells: programmed
◦ No activation as with cytotoxic T cells
◦ Inhibition with contact of normal host MHC molecules
Antigens“molecule that reacts with antibodies or
receptors on B and T cells”
Immunogens-antibodies Epitope – antigenic determinant
(recognized) Paratope – Ag binding site (antibody or
lymphocyte)
Antigens Self-antigen – every cell*, genetically
determined (MHC), HLAs+
*glycoproteins – not RBC+ human leukocyte antigens
Tolerance
Humoral* Immune Response
Antibodies◦Immunoglobulins
◦Plasma cells◦Classes IgG, IgA, IgM, IgE and IgD
*fluid
Classes of ImmunoglobulinsIgG
◦Most abundant (80 to 85%)◦Transported across the placenta◦Four classes
IgA◦Two classes IgA1 – blood IgA2 – body secretions
Classes of Immunoglobulins• IgM– Largest– First Ab produced during 1° response to an Ag– Synthesized during fetal life
• IgD– Low concentration– Ag receptor on surface of early B cells
• IgE– Allergic responses– Parasite infections
Functions of Antibodies Direct effects
◦ Neutralization◦ Agglutination◦ Precipitation
Indirect effects◦ Opsonization◦ Complement
B Cell Antigen Receptor
Surface of B cell Consists
◦ Antigen – recognition molecule : IgM,IgG monomer
◦ Intracellular signaling molecules
Cell Mediated Immune Response• Mature T cells
–1.Cytotoxic (Tc) – attack and destroy directly
–2.Regulatory helper T (Th) – controls• Cell mediated• Humoral mediate• Suppressors (Ts)
–3.Memory cells“viruses, tumors, pathogens resistant to
neutrophils and macrophages”
T Cell Recognition of a Target Cell
T cell receptor complex◦ Antibody-like transmembrane protein◦ Accessory proteins for intracellular signaling
Antigen presentation molecules◦ By antigen presenting cells◦ Major histocompatibility complex (dendritic
cells*, macrophages, B-lymphocytes)◦ *Nobel Prize Medicine & Physiology 2011:
Beutler, Hoffman & Steinman
Functions of T-lymphocyte “Killing abnormal cell”
◦ Cytotoxic T lymphocytes (viruses, tumors) Attach to target cell : MHC-I molecules Appropriate CD molecules
Activate macrophages◦ Cytokines – chronic inflammation
Regulate immune response◦T-helper (Th) cell – humoral & cellular◦ T-suppressor cells – affects immune
response
Primary and Secondary Immune Responses
Primary◦Initial exposure◦ Latent period (B cell differentiation)◦ After 5 - 7 days – IgM antibodies detected◦ An IgG response follows
Primary and Secondary Immune Responses
Secondary◦ More rapid◦ Large amounts of Ab are produced◦ Rapid response - 2° to memory cells◦ IgM – similar to 1° response, IgG – greater
number Figure 6-15 Page 161
◦“MEMORY”
Active vs. Passive Immunity
Active Immunity◦ Antibodies or T cells produced after either a
natural exposure to an antigen or after immunization
Passive Immunity◦ Preformed Ab or T lymphocytes are
transferred from a donor to a recipient.◦ Example: IgG for hepatitis A exposure
: tetanus toxoid
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