Microbes Chapter 27

Specificity of Antigen-Antibody Reaction. Give example

Dependent on lymphocyte receptors interacting with individual pathogen/antigens.

Ex) T cells express antigen-specific receptors called T cell receptors.

Ex) B cells have antigen-specific receptors known as immunoglobulins/C cell receptors. Which bind to unique epitopes on pathogens.

Memory and its result 

Subsequent exposures to the same antigen result in rapid production of large quantities of antigen-reactive T cells or antibodies.

Primary Immune Response 

First exposure to an antigen where antigen recognition by specific B or T lymphocytes leads to B and T cell activation, proliferation, and differentiation.

Second Immune Response

Subsequent exposure to the same antigen activities. Faster, stronger, and all cells ready to go.

Tolerance

Acquired inability to make an adaptive immune response to one’s own antigens discrimination between host and foreign antigens.

Autoimmunity 

Failure to develop tolerance may result in reactions against self.

T Cell Positive Selection

T cells that recognize MHC peptides are retained.

T Cell Negative Selection

T cells that pass the positive selection and strongly bind to self antigens are selected against. 

Clonal deletions

More than 99% of T cells that enter the thymus do not survive the selection process. Remaining T cells react strongly with foreign antigens.

B Cell Positive Selection. Give 3 examples

Occurs when the B cell receptors encounter an antigen that they recognize.

Proliferate- making more copies.

Differentiate- into memory cells and plasma cells.

Produce proteins- antibodies.

B Cell Negative Selection

Occurs in the bone marrow where self-reactive B cells are deleted (clonal deletion) or silenced (clonal anergy) because they lack a T cell help signal. 

2 Classes of Adaptive Immunity

Active and passive

How is active immunity generated?

Generated from exposure to an antigen. Develops memory cells. Therefore producing long lasting immunity.

Passive Immunity

Transfer of antibodies or immune cells. Consist of pre-formed antibodies or cells. Rapid effect. No lasting immunity. 

Natural Adaptive Immunity

Getting a disease and recovering.

Natural Passive Immunity

Passing premade antibodies to nursing infants through breast milk.

Artificial Active Immunity

Receiving a vaccination shot and developing immunity.

Artificial Passive Immunity

Receiving pre-formed antibodies (antiserum). 

Antibody or Immunoglobulin

Soluble protein made by a B lymphocyte or plasma cell in response to antigen exposure. 

5 Classes of Antibodies or Immunoglobulins

IgG, IgA, IgM, IgD, and IgE.

IgG: Define + Structure

Most common antibody circulating in the body.

HC: 3 constant 1 variable (4 polypeptides total).

LC: 1 constant 1 variable. 

IgM: Define + Structure

First to be made after infection. It is also the largest antibody. Pentamer. Providing early immune response.

HC: 4 constant 1 variable (5 polypeptides total).

LC: 1 constant 1 variable (2 polypeptides total). 

IgA: Define + Structure

Present in body fluids like saliva, tears, breast milk, colostrum, and mucosal secretions. Plays crucial role in mucosal immunity by preventing pathogens from adhering to and penetrating epithelial cells.

HC: 3 constant 1 variable (4 polypeptides total).

LC: 1 constant 1 variable (2 polypeptides total).

IgE: Define + Structure

Found in serum and functions as an antibody that binds eosinophils.

HC: 4 constant 1 variable (5 polypeptides total)..

LC: 1 constant 1 variable (2 polypeptides total).. 

IgD: Define + Structure

Present in serum. Regulatory function like beta. Not much known

HC: 3 constant 1 variable (4 polypeptides total).

LC: 1 constant 1 variable (2 polypeptides total).

Which immunoglobulin structures have 3 constants on heavy chain and 1 constant on light chain (4 polypeptides total)?

IgG, IgA, and IgD.

Which immunoglobulin structures have 4 constants on heavy chain and 1 constant on light chain (5 polypeptides total)?

IgM and IgE.

Binding Affinities

Different antibodies bind their epitopes with different strengths. 

How does the immune system generate an almost unlimited antibody variation?

Through somatic recombination, hypermutation, random heavy and light chain reassortment, and coding for joint diversity.

Causes of Hypermutation

Causes changes in binding affinity that, when combined with decreasing antigen concentration, causes affinity maturation.

Affinity Maturation

The strengthening of antibody binding as the immune response progresses.

Clusters of Differentiation (CD)

Cell surface molecules expressed on the cells of immune system.

What role do CD play?

Key role in cell to cell communication, sensing the microenvironment, and in adaptive immunity.

When do immune cells express complex variations of CD antigens on its cell surface?

During lymphocyte maturation. 

CD Markers on T Helper Cell 

CD4

CD Markers on T Regulatory Cell 

CD4

CD Markers on Cytotoxic T Cell 

CD8

Major Histocompatibility Complex (MHC) I

Present internal antigen to CD8 T cells (cytotoxic). Cell targeted for destruction by T cells.

Major Histocompatibility Complex (MHC) 1 Location

Found on all nucleated cells except blood cells.

MHC 1 is a major antigen barriers for _______

Tissue transplantation. 

Major Histocompatibility Complex (MHC) II

Present internalized antigen to CD4 T cells.

Major Histocompatibility Complex (MHC) II Location

Found on surface of the antigen presenting cells (APC): B lymphocytes, macrophages, and dendritic cells. 

What does MHC II activate? Receive?

Activate T helper cells. Receive T cell help. 

Th1

Activates macrophages. Secrete cytokines. Play a role in inflammation and rejection of transplanted organs.

Th2

Plays key role in B cell activation and antibody production.

Treg Cells

Suppress immunity and inflammation.