Microbiology Chapter 18: Specific Adaptive Host Defenses

Specific immunity

• Adaptive immunity that is acquired after an immunization event

• Can be a vaccine or infection

Immunocompetence

• The ability of the body to react with countless foreign materials and mount a response to clear it

Immunocompromised

• The inability of the body to react with countless foreign materials and mount a response to clear it

Specificity

• The fact that immune properties only work against the specific pathogens they are made to fight

• Ex: Immune properties related to measles won’t work against the common cold

Memory

• The ability of immune cells to be recalled to action once the body is faced with the pathogen they are

Antigens

• Anything that can stimulate an immune response

• Typically a protein or peptides

Immunogen

• An antigen that does stimulate an immune response

Antibodies

• “Immunoglobulins”

- Appreciated as IG

• Y shaped protein

• Present on the surface of B cells, secreted into the blood, or lymph

• Triggered by an immunogen

• Binds to of antigen epitopes

Epitopes

• The part of the antigen that the antibody can bind to

• Multiple per pathogen

T cells

• Immune cells

• Initially form in bone marrow

• Develop in thymus

• Subdivided

- Helper T cells

- Regulatory T cells

- Cytotoxic T cells (Killer T cells)

Helper T cells

• Immune cell

• Turns on other immune cells

• Have CD 4 markers

• Activated by APCs

• Interact with MHC II

Regulatory T cells

• Immune cell

• Down regulates immune response

• Have CD4 markers

• Activated by APCs

• Interaction with MHC II

Cytotoxic T cells

• Immune cell

• “Killer T cells”

• Have CD8 receptors

• Interact with MHC I receptors

- On all cells but red blood cells

• Act as marauders that test for potential threats and eliminate them as needed

B cells

• Immune cell

• Developed in the bone marrow

• Makes antibodies

T and B Cell Development

• Hematopoietic stem cells

• Lymphoid stem cells

• Immature lymphocytes

Thymic selection

• Process to select only the competent T-cells

• Done in the cortex of thymus

• Development of TCR

• Interaction of MHC

• Self check

Marker

• Part of the T cell

• Works with MHC to allows for communication with other T cells

TCR

• “T cell receptors” or “Marker”

• Developed in the cortex of the thymus

• Somatic recombination rearranges the genes that encode the TCR

- Allow for different cells to recognize different things

MHC

• “Major Histocompatibility Complex”

• Part of thematic selection

• Located on other cells

• Set of genes that encode the ability for genes T cells to recognize pathogens

• Determine if T cells will become helper or cytotoxic cells

- MHC2: Helper and regulatory t-cells, cause CD4 production by TCD

- MHC1: Cytotoxic t-cells, cause CD8 production by TCD

Apoptosis

• Programed cell death

Th2

• Type of helper T cell

• Stimulate B cells and other T cell activation

Th1

• Type of helper T cell

• Stimulates macrophages and natural killer cells

B cell development

• Mature in bone marrow

• Positive selection for cells that have normal receptors

• Negative selection of B cells that recognize “self”

• They then go to the spleen to undergo somatic

  recombination

B cell activation without T help

• T cell-independent activation

- Only happens with T-independent antigens

- Doesn’t need T cell help

• No memory produced

T-independent antigens

• Antigens that have repeats on the surface like LPS

- Allows for multiple BCR to bind

BCR

• “B-cell receptor”

APC engulfment of pathogen

• First step of B-cell activation with T-cell help

• Engulfs the pathogen

• Degrades the pathogen

• Display peptides on MHC II

Activation of helper T cells

• Second step of B-cell activation with T-cell help

• Stimulates B-cells to grow and divisions

APC

• “Antigen presenting cell”

• Present antigens to the immune system

- Use their MHC2 receptors to do this

• The phagocytic cells

- Dendrites

- Macrophages

• Move to lymph nodes once loaded with antigens to activate helper T cells

B cell activation with T help

• First step: APC engulfment of pathogen

- Engulfs the pathogen

- Degrades the pathogen

- Displays peptides on MHC II

• Second step: Activation of helper T cells

- T cells grow and divide

• Third step: T cell activation of B cell

- T cells activate the B-cells

• Produces immune memory

MHC II

• Complex on B cells

Plasma cells

• Immune cells that secret antibodies to fight pathogens

Class switching

• The act of immune cells becoming even more specialized

- Happens as a result of somatic hypermutation

• Makes antibodies more effective

- More affinity and better breadth

Opsonization

• The tagging of pathogens

Neutralization

• Binding of pathogens

• Stop action

Agglutination

• The sticking of multiple pathogens

• Stops activity

• Makes for easy elimination

ADCC

• “Antibody-dependent cell mediated cytotoxicity”

• Attaches to pathogen that is two large to be consumed

• Signals cytotoxic T cells to come over and releases their cytotoxins into the pathogens

- Death by a thousand paper cuts

Constant region

• Part of antibodies, TCR’s, or BCR”s

• Are always the same between similar cell types

Variable region

• Part of antibodies, TCR’s, BCR’s

• Are always different, even between same cell types

Somatic recombination

• Part of the development of TCR

• Allows for genetic variance between the TCR of T-cells

- T-cells can sense different things

Development of TCR

• First stage of thematic selection

• T-cells begin to make their receptors

• When somatic recombination happens

Interaction of MHC

• Second stage of thematic selection

• Newly developed TCR interact with MHC to check their functionality

- If can bind then they move on

Self check

• Third stage of thematic selection

• Makes sure T-cells don’t recognize self as bad

Interlekin 1 (IL1)

• A cytokine that is secreted by APC

• Stimulates growth of the bound cell

Interlekin 2 (IL2)

• A cytokine that is secreted by the helper T cell that received interlekin 1

• Stimulates growth of all kinds of T cells

IgG

• Type of antibody

• Shaped like a Y

• Very prominent in the blood stream

• Can cross the placenta barrier

IgA

• Type of antibody

• Shaped like a two Y’s stuck together, bottom to bottom

• Very prominent in the secretions

- GI tract

- Respiratory tract

MCH I Receptor

• Located on plasma membrane of all nucleated cells

- All cells but red blood cells

• Used to declare health or illness of cell

- When healthy “self” proteins are displayed

- When ill “other” proteins are displayed

• Cytotoxic T cells read these receptors to determine if they should kill the cell or not

IgM

• Antibody class

• Produced as part of the inmate immune response