MAJOR HISTOCOMPATIBILITY COMPLEXMHCs: The Role of Cell Surface Markers

MHC-MAJOR HISTOCOMPATIBILITY COMPLEX Immunity = ability to distinguish

between "self" and "non-self” Every cell carries same set of distinctive

surface proteins distinguish you as "self”

Pattern is unique to individual

Set of unique markers on human cells = major histocompatibility complex (MHC).

IMMUNE RESPONSE Respond against/eliminate foreign

agents

Protein toxin moleculeVirus Infectious bacterium

Lack of MHC = Lack of immune response

HISTOCOMPATILIBITY Similarity of patterns of MHC molecules

Skin graftsTissue/organ transplants

Organ transplantsBoth individuals examined for genetic

similarityBlood group & MHC molecules 10/12 matchesMedicine to lower immune response

MHC CLASS I/II Inherit 2 of each class (MHC I/II)

1 from Mom1 from Dad

Both sets of Class I or Class II OR sometimes both are expressed on cell surface

Induction of immune response of invader

Class (I/II) expressed on surface depends on type of cell involved

MHCS

WHICH CELLS EXPRESS MCH I/II? All nucleated cells = equally express

BOTH sets of just MCH I

ANTIGEN-PRESENTING CELLS Some specialized cells

of immune system = express BOTH sets of MCH I AND MCH II B-lymphocytes Macrophages Certain dendritic cells

Capacity to express MHC Class II molecules known as Antigen-Presenting Cells (APC)

ANTIGEN-PRESENTING CELLS Can present parts of proteins taken up

by the ACP to T lymphocytes.

NON-SPECIFIC MECHANISM First line of defense

Physical barriers of the body Skin Mucous Tears Saliva pH of skin

NON-SPECIFIC MECHANISM 2nd line of defense

White blood cells + inflammatory response Phagocytosis (Neutrophils, macrophages,

eosinophils) Inflammation = blood supply increased in injured

area (redness, heat)Swelling = histamine released by basophils

and mast cells, triggers inflammatory response

SPECIFIC IMMUNE MECHANISM Recognizes SPECIFIC foreign material and

destroys itAntibodies, Killer T cells

Active vs. Passive immunity Active = develops after recovery disease or

vaccination Chicken pox, vaccinations (measles, mumps, rubella)

Passive = passed from one individual to another NOT PERMANENT!

Ex: Breast-feeding passes immunities to child

2 TYPES OF RESPONSES TO ANTIGENS

1. Humoral immunity-B Cell activation-Production of antibodies

2. Cell-mediated response- Production of Cytotoxic T Cells

HUMORAL IMMUNE RESPONSE Antibodies produced Bind to antigens = easier targets for

phagocytes. Mainly free bacteria, toxins, viruses in body

fluids

HUMORAL RESPONSE

HUMORAL RESPONSE T-Cell (Helper T Cell)

Specifically interacts with MHC II shapes produces cytokines

Cytokines (IL-2) stimulate activated B cells to produce antibodies

Now, anywhere toxin is in system… engulfed by macrophages!

CYTOKINES Secreted proteins + signaling molecules Interleukin

promote development and differentiation of T & B cells

Interleukin-1 (IL-1) Inflammatory response (fever) Macrophage secretes IL-1 after presenting

antigen IL-1 + presented antigen Activates helper T

Cell to produce IL-2

CYTOKINES Secreted proteins + signaling molecules Interleukin

promote development and differentiation of T & B cells

Interleukin-1 (IL-1) Inflammatory response (fever) Macrophage secretes IL-1 after presenting antigen IL-1 + presented antigen Activates helper T Cell to

produce IL-2

Interleukin-2 (IL-2) “The Recruiter” Helps B cells that have contacted antigen to

differentiate into antibody-secreting plasma cells Helps Cytotoxic T cells become active killers

CELL MEDIATED IMMUNE RESPONSE Cytotoxic T cells

(Killer T cells) produces killer substances

Active against viruses/bacteria within infected cells Will be eliminated

from the body Depends on MHC

Class I AND II

CELL MEDIATED IMMUNE RESPONSE

Viral proteins associate with MHC I Transported to surface

Recognized by cytotoxic T cell (Killer T Cell) Binds to specific fragment

shape of MHC I and foreign protein shape (FITS TO ONLY FOREIGN)

ACTIVATES AND PREPARES KILLING SUBSTANCES

Waits for permission from Helper T cell

CELL MEDIATED RESPONSE Helper T Cell

Activated by interaction of APC (Antigen Presenting Cell) presenting fragments via MCH II molecules Just like in Humoral Response!

Helper T Cell releases cytokines (IL-2) SIGNALS KILLER T CELL

TO RELEASE THE KILLING SUBSTANCES!

Kills cell that contains virus Eventually rid body

ORGAN TRANSPLANTS MHC Class I / II expressed on

surface of tissueDifferent shapes than our ownRecognized by helper and killer T cells

See it as out own MHC molecules “presenting” foreign fragments

Perceived as our own tissue that is “infected”REJECTION-IMMUNE SYSTEM ATTACKS!

10/12 MHCs must match Immunosuppressant medication