2. Immunology

Innate immunity

part of the immune system that you were born with

Adaptive immunity

activated by a foreign substance or pathogen

First line of defense against any pathogen

Innate immune system

Components of innate immunity

Phys/Chem barriers
Complement system
Innate immune cells

Most important part of innate immune system

Physical barriers of skin and mucosa

Physical barriers also include

enzymes and acids in tears, mucosa, and GI tract

Complement system

a group of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism.

First function of comp system

Cause lysis of pathogens

Second function of comp system

Opsonize pathogens for destruction Op

Opsonize

to mark pathogens for destruction by phagocytes, enhancing their visibility and uptake.

Third function of comp system

Promote inflammation and recruit immune cells.

Classical compliment pathway

triggered by IgG or IgM antibody-antigen complexes

Lectin comp pathway

activated when lectin binds mannose sugars on pathogen membranes

Alternative comp pathway

activated when C3b binds to a pathogen surface

How do all 3 compliment pathways converge

the formation of distinct C3 convertases

Neutrophils aka

polymorphonuclear cells (PMNs)

polymorphonuclear cells

Most common wbc

Neutrophils are best against

extracellular pathogens

3 ways neutrophils kill pathogens

Phagocytosis
DNA NETS
Degranulation

Phagocytosis

engulfment and digestion of a bacteria

DNA NETs

extracellular traps formed by neutrophils to ensnare pathogens and facilitate their destruction.

Degranulation

release of toxic enzymes, proteases, and reactive oxygen species (ROS) to kill pathogens

Reactive oxygen species

Superoxide
Hydrogen peroxide
Hypochlorite

Superoxide

O₂-

Hydrogen peroxide

H₂O₂

Hypochlorite

HClO^-

How do neutrophils recognize bacteria

Neutrophils and macrophages have pattern recognition receptors (PRRs) to identify common structures on bacteria

Pattern recognition receptors PRR

recognize pathogen associated molecular patterns (PAMPs)

Can PAMPs be found on human cells

No, they must be unique to pathogens for distinction

Toll-like receptors (TLRs)

PRRs that recognize specific PAMPs on pathogens.

TLR4

recognizes LPS

TLR5

Recognizes flagella

Bacterial capsule

Polysaccharide layer to protect bacteria from innate immune system

Why is the capsule so good for immune evasion

humans also have polysaccharide layers, so there is no PRR (TLR) to recognize capsule

Mast cells

release granules that release histamine during allergic reaction

Natural killer cells

recognize cells that have an intracellular infection or are potentially cancerous

Common indication of intracellular infected cell

Downregulated MHC I on the cell surface to prevent infection from being discovered

Monocyte

Precurser to macrophages or dendritic cells that circulate in blood

Macrophage

Phagocytic cells that engulfs and digests foreign substances and pathogens

Phagocytosis

Phagosone fuses with lysosome to degrade substance into antigens

MHC specificity

Nonspecific to antigen, so they will bind to anything

MHC I

Found in all nucleuated cells that presents endogenous antigens to cytotoxic T cells.

MHC II

Found on antigen presenting cells: macrophages, dendritic cells, and b cells that presents exogenous antigens to helper T cells.

Antigen presenting cells- function

group of immune cells that can process and present antigens to T cells to begin the adaptive immune response.

Main antigen presenting cells

include dendritic cells, macrophages, and B cells.

unique thing about red blood cells

Do not have a nucleus or MHC class I molecules.

MHC stands for

major histocompatibility complex that bind to antigens and display them for T cell recognition to activate immune response

Downregulation of MHC I is recognized by

NK cells

Adaptive immunity is

generated as a person encounters foreign substances, thus each person’s adaptive immunity is unique

Adaptive immunity cells

B and T cell

Each B cell

Produces a unique antibody

Antibodies recognize

A singular epitope

Top of the Y shape in antibody

Antigen binding site (Fab)

Bottom of the Y shape in antibodies

is the constant region (Fc) that determines the antibody's class.

Membrane attack complex (MAC)

is a structure formed by complement proteins that creates pores in the membranes of target cells, leading to cell lysis.

IgM

pentamer which is produced first during an immune response.

IgG

Found in blood and is best at fighting infections

IgA

found in mucous membranes and fluids like breastmilk. Best for opsonization

IgE

Parasitic worms and allergies

IgD

Activates mast cells and basophils, relatively unknown

T cells

Cytotoxic and helper T cells that play crucial roles in the adaptive immune response by recognizing antigens and coordinating the immune system.

Cytotoxic T cells

kill infected or damaged cells

Helper t cells

Help B cells make antibodies and help activate cytotoxic T cells

What type of cells are killed by cytotoxic t cells

Infected, damaged, cancerous cells

CD8

T cell receptor found on cytotoxic t cells

Possible functions of helper t cells

Stimulate B cells, activate T cell, cytokine release (inflamm.)

CD4

T cell receptor found on helper t cells

T and B cell receptors look like

Y shape just like antibodies but specifically recognize antigens.

Genetic recombination for B and T cells

During B and T maturation, they each develop unique B and T cell receptors through a process of gene rearrangement that allows for the diversity of antigen recognition.

CD8 recognizes

MHC class 1

CD4 recognizes

MHC class II molecules

B cell antigen presentation

Presents to helper T cell (CD4), and then it will release cytokines in order to activate B cell to proliferate into memory B cell and plasma

Plasma cell

Long lived cell that makes all anitbody classes

Memory B cell

Remembers antigen for decades to mount quick response

T-cell independent B cell activation

If many BCRs are activated, B cell can differentiate into short lived plasma cells that secretes IgM