Chapter 15 Microbiology

Adaptive, Specific Immunity and Immunization

Third line of defense is usually

acquired

Antigen

Molecules that stimulate a response by T and B cells

Two features that characterize specific immunity

specificity and memory

Functions of receptors

1. perceive and attach to non-self or foreign molecules

2. promote the recognition of self molecules

3. receive and transmit chemical messages among other cells of the system

4. aid in cellular development

MHC class I Receptors location

all cells except RBCs

MHC class II Receptors location

limited to WBCs

Function of MHC

plays role in recognizing recognization of self and rejects foreign tissues

Function of MHC Class I

• regulates immune reactions

• required for CD8 Cytotoxic T-lymphocyte antigen presentation and CD8 T cell activation

Site of lymphocytic stem cell differentiation

bone marrow

When lymphocytic stem cells differentiate, they differentiate into these types of immune cells

pre-B and pre-T cells

pre-B cells stay in the bone marrow and become this type of B cell

naïve B cells

T cells migrate to this gland for maturation

thymus gland

Both T and B cells migrate to secondary lymphoid tissues to encounter antigens and become

• Activated T cells

• Plasma B cells

B-cell receptors typically bind ____ antigens

free

T-cell receptors typically bind _____ antigens along with MHC molecules

processed

Immunoglobulins

large glycoproteins that serve as specific receptors of B cells

Receptors of B cells

immunoglobulins

Chemical composition of immunoglobulins

• 4 polypeptide chains

  • 2 identical heavy chains

  • 2 identical light chains

• Y-shaped arrangement

When the B cell receptor is secreted it is called an

antibody

T-Cell Receptors for Antigen

• 2 parallel polypeptide chains, most commonly alpha and beta chain

• small, not secreted

Different classes of T-cell receptors are termed

CD (cluster of differentiation)

Types of CD

CD4 and CD8

Location of CD4

T-helper cells/helper T cells

Location of CD8

Cytotoxic T-cell/Cytotoxic T-lymphocyte

How B and T cells interact

1. B-cells finds an antigen which matches its receptors

2. It waits until a T-helper cell activates it

3. B-cell divides into plasma and memory cells

4. Plasma cells produce antibodies that attach to invader

Plasma cells produce

antibodies

How CD4 Helper T cells are Activated

1. Phagocyte eats bacteria

2. Parts of the bacteria (antigen) goes to the surface of phagocyte

3. Phagocyte presents antigen to a helper T-cell

4. Helper T-cell is activated

Function of T-cells (CD4)

recruit neutrophils, kills helminthes

CD8 T cell Activation is caused by

• binding of MHC I presenting an antigen

• helper CD4 T-cells

Function of perforins in cytotoxic T cells

punch holes in target cells

Function of granzymes in cytotoxic T cells

cause apoptosis

Antibody-Antigen Interactions

• opsonization

• neutralization

• antibody tagging

• complement fixation

Opsonization

binding of antibodies or complement proteins to the surface of infected cells or directly to the microbes

Neutralization

Abs fill the surface receptors on a virus or the active site on a microbial enzyme (ex. C. tetani toxin) to prevent it from attaching

Antibody tagging increases the rate of

phagocytosis

Complement fixation

activation of classical complement pathway, results in rupturing of cells and some viruses

IgM

• 5 monomers

• first synthesized following Ag encounter

• Can serve as B-cell receptor

Immunoglobulin responsible for first line of defense

IgM

IgG

• monomer

• produced by plasma cells

• most prevalent

Which immunoglobulin is produced by plasma cells

IgG

These immunoglobulins require class switching

IgA, IgD, IgE

IgA

monomer circulates in blood, dimer in mucous and serous secretions (membrane bound and secreted), found in GI and respiratory tract, passed to newborns in breast milk

Immunoglobulin found in breast milk

IgA

IgD

monomer, serves as B-cell receptor for antigen on B cells

Which immunoglobulin serves as a B-cell receptor

IgD

IgE

• monomer

• responsible for allergic responses and worm infections

When an infection passed, _____ cells undergo apoptosis, and _______ _____ cells remain

plasma cells, specialized memory cells

Primary response to Antigen

after first exposure to an Ag immune system produces IgM and a gradual increase in Ab titer (concentration of antibodies) with the production of IgG

Secondary Response to Antigen

immune system produces a more rapid, stronger response due to memory cells

Anamnestic response

renewed rapid production of an antibody on the second or subsequent encounter with the same antigen

All antibodies in the IgA class

Have identical Fc regions

Antigenicity

property of behaving as an antigen

Characteristic of antigenicity

Foreignness, size, shape, and accessibility

Characteristics of Antigens

• foreign

• epitope

• immunogens

• antigenic determines

Epitope

small molecular group that is recognized by lymphocytes/antibodies

Haptens

small foreign molecules that consist only of a determinant group

Special Categories of Antigens

• superantigens

• allergens

• autoantigens

Superantigens

potent T cell stimulators; provoke an overwhelming response

Allergens

antigen that evokes allergic reactions

Autoantigens

molecules on self tissues for which tolerance is inadequate

Active immunity

results when a person is challenged with antigen that stimulates production of antibodies; creates memory, takes time, and is lasting

Passive immunity

preformed antibodies are donated to an individual; does not create memory, acts immediately, and is short term

Natural immunity

immunity acquired as part of normal life experiences

Artificial immunity

acquired through a medical procedure such as a vaccine

Treatment of choice in preventing measles and hepatitis A and in replacing antibodies in immunodeficient patients

passive immunity

Sera available for diphtheria, botulism, and spider and snake bites are produced by this animal

horses

Vaccination is identified as this kind of immunity

artificial immunity

Artificial active immunity

deliberately exposing a person to material that is antigenic but not pathogenic

Qualities of an Effective Vaccine

• low level of adverse side effects

• protect against exposure to natural and wild forms of pathogens

• stimulate B and T cells

• long lasting effects

• should not require doses and boosters

Vaccines are usually prepared with

1. killed or inactivated viruses

2. alive, active cells or viruses

3. antigenic molecules derived from bacterial cells or viruses

4. genetically engineered microbes or microbial agents

5. mRNA

Killed or Inactivated Vaccines

• Cultivate the desired strain, treat it with formalin or some other agent that kills the agent but does not destroy its antigenicity

• often require a larger dose and more boosters to be effective

Attenuation

process that substantially lessens or negates the virulence of viruses or bacteria

• eliminates virulence factors

Attenuated vaccinates usually have (lower/higher) doses and boosters

lower

Capsules are found in

pneumococcus, meningococcus

Surface proteins are found in

anthrax, hepatitis B

Exotoxins are found in

diphtheria, tetanus

Genetically Engineered Vaccines

Insert genes for pathogen’s antigen into plasmid vector, and clone them in an appropriate host

DNA vaccines create recombination by

inserting microbial DNA into plasmid vector

Examples of genetically engineered vaccines

Lyme disease, hepatitis C, herpes simplex, influenza, tuberculosis, malaria

If the capsule of the pathogen is being used as a vaccine, it would be called a/an

acellular vaccine

Some vaccines require addition of an ________ to enhance immunogenicity and prolong retention of antigen

adjuvant

Possible side effects of vaccination at local site

• fever and allergies

• rarely, mutation and neurological effects happen

Herd Immunity

concept that immune individuals will not harbor a pathogen, thus reducing the occurrence of pathogens

• makes it less likely for a nonimmunized individual to encounter pathogens