Microbial Disease

Two types of Immunity

Innate and Adaptive

Innate

- No specificity

- Cells:

Lymphoid cells (Natural Killer cells)

Phagocytes

Adaptive

-Specificity

-Cells:

T & B lymphocytes

Whats the purpose?

Limit Entry and Growth

How to limit entry?

Skin

Membranes

Flora

Skin

Impermeable

hostile

sweat (lactic acid)

low pH

Membranes

Mucus

cillia

antimicrob flushing

Flora

competition

inhib compounds

How to limit growth?

bacteria killing enzyme

phagocytosis

Two types of phagocytes

macrophages

neutrophils = polymorphs

Macrophages

Promonocytes (bone)> monocytes (blood) > macrophage (tissue)

lung, liver, lining of lymph nodes

Polymorphs

White cells

Non dividing

No mitochondria

Phagocytosis (PAMPs and PRRs)

Pattern Recognition

PAMPs: pathogen associated molecular patterns

PRRs: pathogen recognition receptors

How does a phagosome form?

pseudopodia extend out, actin myosin close, phagosome forms

2 Types of fusion and killing

oxygen-independcent (other mechanisms and enzymes)

oxygen-dependent (using bunch of intermediates)

Compliment system of Phagocytosis

Contact > Formyl Methionyl peptides attracts leukocytes (chemotaxis) > Compliment proteins

Compliment system

product > catalyst of next

C followed by # (ex C3)

Explain the C3 complement system

C3 to C3a & C3b

C3b > C3bB > C3bBb (c3 convertase)

More pathogen, more stabilized and breakdown occurs more

Alternative Complement Pathway (C5 C3 pathway)

1. C3b bind to bacteria (marks bacteria)

2. C5 forms complex with C3a 

   • chemotactic factors (attracts bacterial cell)

   • vascular permeability mediatiors (allows macrophage travel)

Poking hole pathway

MAC: membrane attack complex

C3bBb makes C5a leave (later forms complex with C3a)

C3b and C5b left, recruit C6-8 then C9

creates hole

Acute Phase Proteins

Increase in concentrations in response to injury and inflammation

Not specific, used as indications

Antimicrobial Factors

Act in phagocytic cells and in fluids

Tears and Saliva (Lysozyme) 

Lactoferrin (blood, iron binding compound sapping iron from pathogens)

Interferons

Cells infected resistant to superinfection

Secrete interferons, which bind to other cell receptors, leading to producing antiviral proteins to limit spread.

Natural Killer Cells

Bind to receptors of cell, cell release granules like MAC (membrane attack complex)

Allows entry of granzyme B, leading to apoptosis

Eosinophils

Combat large parasites (since too large to be engulfed)

Bind to C3b to activate, toxic compounds released.

Antigen

any molecule that reacts with Ab or Ag receptor

Immunogen

Ag that can induce IR

Antigenic/immunogenic

Relative ability of Ag to induce IR, how good or strong it induces it.

Antigenic determinants = epitopes

Regions of Ag molecule recognized by adaptive immune response

10 or more aa, antigenic structure

thats why mutations are tricky, just need to change the sequence of 10 amino acids

Antibody

produced by b-lymphocytes (b-cells) which produce only one specificity

Neutralizes

In response to Ag divides and differentiates

some to memory cells some to antibodies

Antibody Structure

Two regions (2 arms and stem)

Arms bind

Stem tags for destruction (creates link)

What is antibody made of? (tell me the two and the classes)

Light Chain: either lambda (λ) or kappa (k) since both are identical. Lλ or Lk

Heavy Chain: 5 types, giving the class

μ (mew)=IgM

Y (gamma)= IgG

α (alpha)= IgA

δ (delta) = IgD

ε (epsilon)= IgE

IgG

Y (gamma)

monomeric, 75% of antibodies

4 subclasses based on aa of heavy chain c regions

IgG1-4, IgG1 most

Functions:

Opsonization (marking for death)

Neutralizes

Secondary response

Crosses placenta (w mom)

IgM

μ (mew)

Monomeric (attached to b cell) pentameric in serum held by j chain

Functions:

First Ab during primary response (indicate if been exposed)

Ag receptor on b cell

activate part of innate

clumps particulate antigen (e.g bacteria)

IgD

δ (delta)

monomeric, <2%

\Serum and B cell surface

Unknown Function

IgA

α (alpha)= IgA

monomeric but dimeric in sercretions, low amount

Primary Ab of mucous membranes

Secondary Ab in mucosal secretions (resistant to lac protease, in saliva)

Functions:

Prevent mucous membrane attachment

Passive immunity - breast milk (w mom)

IgE

ε (epsilon)= IgE

monomeric form, low levels

On mast cells (tissues) and basophils (blood)

Functions: 

Anaphylactic Hypersensitivity (alergies, can lead to anaphylactic shock)

Antibody mediated complement pathway

Ab Ag complex trigger C4 > C4b > C4b2 > C4b2a (like C3bBb but for adaptive, breaks down c3)

Shows that they are tightly integrated

Antibody uses

Activate phagocytic cells (trigger phagocytosis)

Neutralization

• blocks virus binding

• blocks bacterium from getting nutrients

• blocks toxic binding

Cell mediated immunity

using Tcells

Ag must be on cell, can’t be free

Its receptor binds to complex of MHC and peptide (taken from pathogen)

T-lymphocytes activate and kill with macrophages (also activated via macrophage activating factors IFNy)

Two major functional population of Tcells

Cytotoxic Tcells:

Tc, infected or cancerous cells CD8

Helper Tcell:

Th, activate b cells and macrophages CD4 (this down=aids)

Th1 Macrophage

Th2 B cells

look at ag presented by MHC class 2

What can T-lymphocytes do?

help macrophages, inhibit intracellular replication

Difference between B and T cells

difference in surface markers (CD). Mature at diff places (not in notes)

B cells

Surface immunoglobin

T cell 

Tcell receptors

Clonal selection and expansion of B-lymphocytes, also why does this happen?

We would need so many Ag and epitopes since it is 1 to 1, not possible.

Correct B-cells (needed Ab) bind to Ag “clonal selection”

Then, “clonal expansion”

Somatic mutations for further tuning

Clonal selection and expansion of T-lymphocytes

No somatic mutations

after expansion some to memory cells

Memory Cells

More readily available and stimulated by Ag

Better combining power, why?

• Bcells, somatic mutations

• Tcells increased expression

Basis for Vaccines

Why are vaccines tricky in regard to toxicity?

Need to keep immunogenicity but cant keep toxicity in. Tricky to deactivate without ruining.

Cytokines

Communication factors

Role:

control of infection

ex. Interferon

Interferon

Infected cell release IFN, attach to uninfected, release antiviral molecules (degrade viral mRNA, Inhibit protein synthesis)

What else do cytokines do in regard to counterbalancing?

help control population of helper T cells

Host-Pathogen relationship 

ability to cause disease vs host ability to eliminate

Adaptation of host and pathogen (length of relationship)

longer the relationship=less damage

myxoma in rabbits

Types of microbial infections

attachment and penetration

biting arthropod

skin wound

Steps of infection

1. Attachment

2. Spread (local)

3. Multiplication

4. Evasion

5. Shedding

6. Damage (not always)

Koch postulates

Suspect germ

Isolated and grown

put into healthy to see if disease

same germ must be reisolated

Challenges of kochs postulates:

Unculturable organisms

Host immunologic factors

More than one pathogen

if only in humans

Molecular evolution of kochs postulates

Virulence trait should be associated with pathogenic strain

Inactivation of that gene should decrease pathogenicity

Replacement of gene with norm should restore pathogenicity

Gene should be expressed at one point

Abs or immune should directed at it should protect

Biological response gradient (severity)

Depends on:

Dose and route (some routes, like skin and gi track need more)

Age (bimodal, young and old)

Sex

Nutritional status

Genetic background

Microbiome

Microbiota + structural elements, metabolites, env conditions

For every human gene how many microbial genes in our body?

350

Role of micorbiota

Nutrient extraction

Metabolism

Immunity (yeast infection)

Making bioactive molecules (vitamins, lipids, aa’s)

Skim microbiota

Lots of variation (oiliness, sweatiness, hairiness, env exposure)

gram + and -

Oily skin: actinobacteria

Moist areas: staphylococcaceae

Dyer: diverse

Most dependant on environment than individual

Vaginal microbiota (transient vs colonizers)

Colonizers (stay)

Lactobacillus acidophillus

Transient (come and go, sexual activity etc)

Staphylococcus epidermis

E.coli

Candida

Enterococcus faecalis

What influences the vag microbiota makeup?

Sex

Diabetes

Antibiotics

Age

Hormones

Oral microbiota

heavily colonized (2nd to colon)

Tongue: lactobacilli

Exposed tooth: streptoccoci

What microbe is inversely related to asthma? Why?

H. Pylori. cagA+ induces an immune response of balancing and preventing over response

Obesity and Microbiota

Antibiotics > microbiota with higher metabolism > extract higher amount (especially foods that were relatively indigestible)

Growth promotion, also thinner intestinal walls (more extraction)

Height and microbiota

Height is increasing in countries that use antibiotics more, correlation not causation. Children with less diarrhea, taller and heavier.

Edward Jenner

Founder of modern vaccination

Small pox vaccine (from cow pox, noticed milk maids didnt get)

Term coined by pasteur in honor, Vacca (latin,cow)