Chapter 16 Microbiology

What is the third line of defense?

the adaptive immune system

Adaptive immunity

the body’s ability to recognize and defend itself against distinct invaders and their products

What are the 5 attributes of adaptive immunity

Specificity, inducibility, clonality, unresponsiveness to self, memory

Specificity in adaptive immunity

will differentiate which bacteria it is and how to fight it off

Inducibility in adaptive immunity

will be off until 1st and 2nd line of defense signal it to activate

Clonality in adaptive immunity

clones antibodies to work better

Unresponsiveness to self in adaptive immunity

will not recognize own body as harmful if works properly

memory in adaptive immunity

reacts faster when you get sick a second time

What are the two main types of lymphocytes?

B lymphocytes (B cells) and T lymphocytes (T cells)

Where do B cells mature?

in the bone marrow

What do B cells do?

produce antibodies

Where do T cells mature?

in the thymus

are natural killer cells also lymphocytes?

yes

What are the two types of adaptive immune responses?

humoral/ antibody and cell- mediated

Humoral/antibody immune responses attach which pathogen

bacterial, fungal or and sometimes viral

Cell-mediated immune responses attach which pathogen

only viral

which lymphocytes respond during Humoral/antibody immune responses

B cells

which lymphocytes respond during cell-mediated immune responses

T-cells

Lymphatic system

always filtering out antigens in the body

Lymph node

have a high concentration of B-cell and T-cells and will only be swollen if infection is present

An antigen is

anything foreign in the body

Epitopes

any structural component of antigen that the body can recognize as foreign

What are the 3 types of antigens?

exogenous, endogenous, and autoantigens

Exogenous antigens

on the outside of a cell, usually bacteria but can be viral as well and was phagocytosed by macrophage and elicits a humoral response

Endogenous antigen

inside a cell so only viruses and elicit a cell-mediated response

Autoantigens

Immune system attacks a part of the own body

Major Histocompatibility Complex (MHC)

receptors that present an antigen to T cells

What are the 2 types of MHC proteins?

MHC class I and MHC class II

MHC class I

found in all nucleated cells, interacts with cytotoxic TCRs and will occur when a virus/endogenous antigen is detected

MHC class II

only on phagocytic cells, interacts with T helper TCRs, exogenous

What type of ligand does MHC I have?

CD8 ligand to activate T cytotoxic cells which send signals to the cell to kill itself before virus begins to replicate

What type of ligand does MHC II have?

CD4 to activate T helper cell to coordinate a response, but cell itself is not infected

what must be processed for MHC proteins to display epitopes?

antigens

antigen processing for exogenous antigens

use MHC II and must be phagocyted

antigen processing for endogenous antigens

uses MHC I and must be internally infected by a virus

What is the function of the MHC I pathway?

to form viral adaptive immune response so that T cytotoxic cells know what they are looking for

What is the function of the MHC II pathway?

to activate B cell response

MHC I pathway

when MHC I + a cell becomes infected with a virus an MHC I obtains endogenous epitope and presents it. Then inactive T cytotoxic cell recognizes presented antigen on the MHC I using a TCR. Then CD8 binds to double check and support the rection to get the immune system ready to go

MHC II pathway

A phagocyte detects a potential pathogen and keeps an antigen of it. MHC II presents an exogenous antigen then an undifferentiated T helper cell binds to MHC II using a TCR. Then CD4 binds to double check and support the reaction to activate the immune system

What makes sure that the B cells and T cytotoxic cells kill the correct thing?

T helper cells

T lymphocytes (T Cells)

circulate in the lymph and blood and migrate to the lymph nodes, spleen, and Peyer’ patches

Where are T cell receptors (TCRs) located?

on the cytoplasmic membrane of T cells

are T cell receptors specific?

yes, they only bind epitopes associated with MHC protein

What are the three types of T cells?

Cytotoxic/killer, helper, and regulatory

Cytotoxic T cells

CD8+ ligand directly kills other cells

Helper T cells

CD4+ ligand functions to “help” regulate the activities of B cells and cytotoxic T cells

T helper 1

helps activate killer cells

T helper 2 cells

help activate B cell

Regulatory

CD4+/CD25+ represses adaptive immune responses

B cells and antibodies

found in spleen, lymph nodes and MALT

what are B cell receptors (BCR)?

surface antibody

What is the antigen-binding sites

the variable region of heavy and light chain

What is the heavy chain of the antibody

the long chains

What is the constant region of an antibody?

anything other than the variable region

activation of complement and inflammation

classical pathway starting via antibody binding

Neutralization

Bind to virus before it binds to our cells by blocking every ligand and preventing virulence

Opsonization

facilitates phagocytosis with Fc receptor

agglutination

clumps pathogen together to concentrate them in one place so immune system can attack them in one place

Antibody-dependent cellular cytotoxicity (ADCC)

activates natural killing cells faster with Fc receptor

IgM

more binding sites, shaped as a pentamer, held together with J-chain and is considered the “first responder”

IgG

most common about 80 to 90% of our antibodies, gamma heavy chain, and stays the longest after infection

IgA

in lacrimal ducts, secretory always, 2 of them together are a dimer with alpha chain

IgE

triggers release of histamine as allergic response and has epsilon chain

IgD

just know that it exists

Interleukins (ILs)

signal among leukocytes

Interferons (IFNs)

antiviral proteins that may act as cytokines

growth factors

proteins that stimulate stem cells to divide

tumor necrosis factor (TNF)

Secreted by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation

Chemokines

chemotactic cytokines that signal leukocytes to move

What are the steps involved in activation of cytotoxic T cells?

Antigen presentation, helper T cell differentiation, clonal expansion, and self-stimulation

Activation of a clone of cytotoxic T cells (virally infected)

If phagocyted, MHC II binds to exogenous antigen which also attaches to the TCR of a T helper cell while CD4 stabilizes it. Then the IL-12 released by the phagocyte differentiates the T helper cell into Th 1 which then releases IL-2. IL-2 then activates T cytotoxic cells. These active Tc cells save a memory T cell and the rest are able to make their own IL-2 to then make more active Tc cells. If virally infected, MHCI bind to an endogenous epitope that is also attached to a TCR of an inactive Tc cell with an IL-2 receptor, this is stabilized by a CD8 ligand. IL- 2s released by Th1 then activate these Tc cells and make more of them.

Perforin

released by Tc cell to make perforin complex that punches holes in the phospholipid bilayer of the virally infected cell so granzymes can go in

Granzyme

activate apoptotic enzymes to induce apoptosis

CD95 glycoprotein pathway

CD95L on the Tc cell recognizes CD95 on a virally infected cell which sends internal signal to activate apoptosis enzymes to induce apoptosis

Memory T cells

persist for months or years in lymphoid tissues and become functional immediately after 1st contact with epitope specific to its TCR

Humoral Immune Responses

against exogenous pathogens and antibodies are the main player

B cell clonal expansion for a humoral response

An antigen presenting cell has a MHC II bound to an exogenous epitope that is connected to the TCR of a T helper cell. This is all stabilized by a CD4 ligand the two cells are connected by a CD18 and CD80 fused ligand. IL-4 differentiates the Th cell into Th2. Th2 cell with a TCR is bound to an exogenous epitope that is then bound to a MHC II of a B cell that are stabalized be a CD4 ligand. Both these cells are connected by CD40L and CD40 which activates B cells. Plasma cells then clone and create antibodies while some become memory B cells

Secondary humoral response

a lot faster than primary humoral response

Naturally acquired immunity

-active: direct exposure by antigen entering body naturally

-passive: antibodies passed from mother to child

Artificially acquired immunity

-active: antigen introduced by vaccines

-passive: antivenoms and antitoxins only long enough to get toxic out of your system