Chapter 15- Host Defenses

What immune defenses are specific vs. nonspecific, and innate vs. acquired?

1st and 2nd : Innate and Nonspecific 3rd: Acquired

The basic immunoglobulin (Ig) molecule contains______ polypeptide chains connected by ________ bonds. Two functionally distinct segments called fragments can be differentiated. The two "arms" that bind antigen are the _____ _____ _____ (abbreviated "Fabs"), and the rest of the molecule is the ______ _______(Fc), so called because it was the first to be crystallized in pure form. The amino-terminal end of each Fab fragment (consisting of the variable regions of the heavy and light chains) folds into a groove that will accommodate one______. The presence of a special region at the site of attachment between the Fab and Fc fragments allows swiveling of the Fab fragments. The ________ fragment serves as an anchor, involved in binding to various cells and molecules of the immune system itself.

4;disulfide; antigen binding fragments; crystallizable fragment; epitope; Fc fragment

What are antigens? What characteristics make a "good" antigen?

AKA immunogens. Substances that provoke an immune response. They are molecules that stimulate a response by T and B cells. In general proteins are very good antigens because of their complex composition.

_________ immunity occurs when an individual receives an immune stimulus (antigen) that activates the B and T cells, causing the body to produce immune substances such as antibodies. Active immunity is marked by several characteristics: (1) It creates a memory that renders the person ready for quick action upon reexposure to that same antigen; (2) it requires several days to develop; and (3) it lasts for a relatively long time, sometimes for life. Active immunity can be stimulated by natural or artificial means.

Active

Explain the activation of T cells and their differentiation into sublets.

After the antigen is presented on the surface of the APC, these cells are ready to activate T cells bearing CD4 markers. This class of T cells is called the T helper class; it bears an antigen- specific T cell receptor that binds to the antigen (epitope) held by the MHC molecule. Once identification has occurred, the APC activates the T helper cell. The T helper cell, in turn, produces cytokine (interleukin IL-2), which is a growth factor for the T helper cells and cytotoxic cells. A stimulated T cell multiplies through successive mitotic divisions and produces a large population of genetically identical daughter cells in the process of clonal expansion. Some cells that are activated stop short of becoming fully differentiated, such as memory cells. However, the con expansion of this cells clone size accounts for the increased speed and intensity of the memory response.

_______ are proteins and other molecules of one person that are antigenic to another.

Alloantigens

How are antibodies made?

Antibodies are produced by specialized white blood cells called B lymphocytes (or B cells). When an antigen binds to the B-cell surface, it stimulates the B cell to divide and mature into a group of identical cells called a clone.

Who "presents antigens"? How are antigens presented in antigen presenting cells and why does this matter?

Antigen Presenting Cells (APC's). - Macrophages - B cells - Dentritic cells All three types of APC's can engulf antigens and process them intracellularly. After processing is complete, the antigen is inserted into a cleft on the MHC receptor and the complex is moved to the surface of the APC so that it will be readily accessible to T lymphocytes during presentation.

________ immunity is protection from infection obtained through medical procedures. This type of immunity is induced by immunization with vaccines or the administration of immune serum.

Artificial

Describe a superantigen.

Bacterial toxin. They are potent stimuli for T cells. (They activate T cells 100 x faster than ordinary antigens). This can result in overwhelming release of cytokines and cell death. ( toxic shock syndrome & certain autoimmune diseases are associated with these)

____-mediated immunities require direct involvement of T lymphocytes throughout the course of the reaction. They are among the most complex and diverse in the immune system.

Cell

What types of markers or proteins (or protein complexes) exist on the surface of immune cells? (for example, MHCs, CDs)

Class 1 MHC Genes: Display unique characteristics of self. Appear on all nucleated cells. *They allow for recognition of self and regulation of immune reactions*. Each human inherits a particular combination of class 1 MHC genes. Class 2 MHC Genes: Code for immune regulatory markers on macrophages, dendritic cells, & B cells. *Involved with presenting antigens to T cells during cooperative immune reactions*. (Like wooden plank of fish ex.) Class 3 MHC Genes: Encode proteins involved with the complement system (See Ch 14). Cluster of Differentiation (CD): Markers important in immunity, found on the membranes of a variety of different cells involved in the immune response. >300 have been described.

______ is a portion of the antigen molecule recognized and responded to by a lymphocyte.

Epitope

What are the 5 classes of immunoglobulins?

G (most common) monomer (2) binding sites A dimer,monomer (4, 2) binding sites M Pentamer (10) binding sites D monomer (2) binding sites E (least common) monomer (2) binding sites

________ are enzymes that attack proteins of target cells.

Granzymes

_______ consists only of a determinant group. Too small by themselves to elicit an immune response. If linked to a carrier group, the *combined molecule* develops immunogenicity. (Only the hapten bound to a carrier molecule develops antibody)

Haptens

______ class of immunoglobulin is a secretory antibody; located on mucus membranes.

IgA

______ class of immunoglobulin is a receptor on b cells.

IgD

______ class of immunoglobulin is an antibody of allergy; & worm infections.

IgE

______ class of immunoglobulin provides long-term immunity; memory antibodies; neutralizes toxins, opsonizes, fixes complement.

IgG

______ class of immunoglobulin is produced at first response to antigen; can serve as a B-cell receptor.

IgM

_______immunity encompasses any immunity that is acquired during the normal biological experiences of an individual rather than through medical intervention.

Natural

______ are recently discovered hybrid type of cell that share properties of both T cells and NK cells. They display T cell receptors and NK cell markers.

Natural Killer T (NKT) cells.

______ are stimulated by glycolipids on foreign cells and rapidly produce cytokines, granzymes, and perforins. They trigger self-destruction in target cells.

Natural Killer T (NKT) cells.

______ are the first killer cells to attack cancer cells and virus infected cells in similar manner to Tc ( Cytotoxic) Cells. & are not considered part of specific cell-mediated immunity because they do not possess antigen receptors.

Natural Killer(NK) Cells

__________immunity occurs when an individual receives immune substances (usually antibodies) that were produced actively in the body of another human or animal donor. The recipient is protected for a short time even though he or she has not had prior exposure to the antigen. It is characterized by (1) lack of memory for the original antigen; (2) lack of production of new antibodies against that disease; (3) immediate protection; and (4) short-term effectiveness, because antibodies have a limited period of function and, ultimately, the recipient's body disposes of them. Passive immunity can also be natural or artificial in origin.

Passive

______ are proteins that punch holes in the membranes of target cells. They cause ions to leak out of target cells, this creates a pathway for granzymes to enter.

Perforins

What makes acquired immunity good?

Provides long-term immunity (ex. chicken pox)

What is the difference between a regulatory cell, a plasma cell, a memory cell?

Regulatory cell: Control T cell response & carry CD4 markers. Acts to control the inflammatory process. Prevents autoimmunity. Makes sure immune response does not inappropriately target normal biota. Plasma cell: are white blood cells that secrete large volumes of antibodies. They are transported by the blood plasma and the lymphatic system. Plasma cells originate in the bone marrow; B cells differentiate into plasma cells that produce antibody molecules closely modeled after the receptors of the precursor B cell. Once released into the blood and lymph, these antibody molecules bind to the target antigen (foreign substance) and initiate its neutralization or destruction Memory cell: a long-lived lymphocyte capable of responding to a particular antigen on its reintroduction, long after the exposure that prompted its production.

What is the difference between a T helper cell (CD4) and a cytotoxic T cell (CD8)?

T helper cells (CD4): Play a central role in regulating immune reactions to antigens. Including B and other T cells. Involved in activating macrophages. Directly by receptor contact and indirectly by releasing cytokines such as interferon gamma (IFNy). *Bind to MHC class II molecules* Cytotoxic T cells (CD8): aka Killer T cells. Must recognize a foreign peptide complexed with self MHC-1 presented to it and mount a direct attack on a target cell. After attack with peferins and granzymes, the targeted cells go through death by apoptosis. *Found on cytotoxic T cells and binds MHC class I molecules*

What types of lymphocytes does our immune system have and how do they develop?

T-cells = develop in the Thymus. Start fight with infection cells or are memory cells, helper cells, or cytotoxic T cells. Cell mediated immunity. B-cells= develop in the bone marrow They are both stored in the lymph nodes and spleen. Produce Antibodies.

Describe cytokines.

They act through receptors, and are especially important in the immune system; cytokines modulate the balance between humoral and cell-based immune responses, and they regulate the maturation, growth, and responsiveness of particular cell populations. Some cytokines enhance or inhibit the action of other cytokines in complex ways.

The _______ _______ occurs with the first exposure to an antigen. The ____ _____ is marked by a lack of antibody production. The antigen is concentrated in the ______ ______. As the ____ ____ produce antibodies, serum titer increases to a ______, then tapers off to a low level over weeks and months.

primary response; latent period; lymphoid tissues; plasma cells; plateau;

The _____ ______ occurs when the immune system is exposed again to the same immunogen weeks, months, or even years later. The rate of antibody synthesis, ___ ______, and length of antibody response is greatly increased over the ____ _____.

secondary response; peak titer; primary response

Define apoptosis.

the death of cells that occurs as a normal and controlled part of an organism's growth or development.

_____ is a term used to describe the body's level of antibodies. It can be measured over time to determine how the immune system reacts to an antigen.

titer