Chapter 17 : adaptive immunity ; specific defenses of the host

Adaptive immunity

defence that target a specific pathogen after exposure

Primary response

first time the immune system combats a particular foreign substance

Secondary response

later interaction with the same foreign substance; faster and more effective due to “memory”

Humoral immunity

• Produces antibodies

• involves B cells

• Best against extrcellular pathogens and toxins

Cellular immunity (cell-mediated immunity)

involves T lymphocytes

Best a fighting virus-infected cells and intracellular bacteria

cytokines

proteins messengers produced in response stimulus

interleukins( ILs)

communicate between leukocytes

Interferons(IFNs)

interfere with viral infections of host cells

Tumor necrosis factor alpha (TNF alpha )

involved in the inflammation of autoimmune disease

overproduction of cytokines leads to a cytokines storm

antigens

substances that causes the production of antibodies usually components of invading microbes or foreign substances

Haptens

molecules too small to be antigenic; attach to carrier molecule and provoke an immune response

Humoral immunity ( antibodies )

four proteins chain form a Y shape

variable ( V) regions ; bind epitopes

constant (Fc) region, which is identical for a particular Ig class

five classes of Ig ( IgG, IgM, IgA,IgD,IgE)

Antigen-antibody complex

forms when antibodies bind to antigens

Protects the host by tagging foreign molecules or cells for destruction

• agglutination

• opsonization

• Antibody-dependent cell-mediated cytotoxicity

• Neutralization

  • activation of the complement system

Major histocompatibility complex ( MHC)

genes encode molecules on the cell surface ( a group of complexes)

Class I MHC

on the membrane of nucleated cells

• identifies a cell as “ self” part of host

Class II MHC

on the surface of antigens presenting cells ( APCs) ←- white blood cells

• on all vertebrates

clonal selection

B Cell is activated when it’s b-cell receptor (BCR) binds to its antigen

Clonal expansion

the activated B cell proliferates and differentiates into plasmocytes ( secrete antibody) and memory B cells

Dendritic cells (DCs)

( APCs) enguld and degrade microbes and display them to T cells

Macrophages

Activated by cytokines or the ingestion of antigenic material

B Cells

Classes of T cells

• CD4+

• T helper cells ( T_H)

• cytokines activate B Cells

• cytokines help activate other cells like

• Bind MHC class II molecules on APCs

• CD8+

• cytotoxic T lymphocytes ( CTL)

  • bind MHC class

T regulatory cells

subset of CD4+ cells; carry an additional CD25 ( what makes them regulatory) molecules suppress T cells against self; protect intestinal bacteria required for digestion ; protect fetus

Superantigen effects

simultaneously bind to MHC II and TCRs

leads to cytokine storm

activation of naive T_c cell

T cell receptor must interact with class I mHC and antigenic peptide endogenous antigen ) presented on another body cell

Activated cytotoxic TActivated lymphocyte ( CTL)

• will recognize other cells expressing the same antigen

• target cells may harbor an intracellular pathogen such as a virus or may be tumor cells or cells in transplanted tissue

• Activated cells CTL attacks target cell with perforin ( forming a pore) , and granzymes ( proteases ) causing apoptosis ,

Apoptosis

programmed cell death

cells cut their genome into fragments, causing the membranes to bulge outward via blebbing

Natural killer ( NK) cells ( puzzle piece )

• innate and adaptive immunity

• destroy virus-infected cell, tumor cells, and attack large, extracellular parasites

• not stimulated by an antigen

• Detect target cells based on whether those cells express MHC class I

Naturally acquired active immunity

resulting from infection

Naturally acquired passive immunity

transplacental or via colostrum

Artificially acquired active immunity

injection of vaccination ( immunization)

Articially aquored passive immunity

injection of antibodies

Vaccine

suspension of an organism or fractions of organisms that induced immune response

provokes a primary immune response

• leads to the formation of antibodies and long-lived memory cells

  • produces a rapid, intense secondary response

Attenuated vaccines

weakened pathogen, reduced virulence

closely mimic an actual infection

confers lifelong immunity ( both humoral and cellular)

not giving to immunocompromised patients

inactivated vaccines

( dead pathogen ) whole microbes are killed or inactivated

safer than attenuated vaccines

require repeated booster doses

induce mostly humoral immunity

subunit vaccines

use antigenic fragments to stimulate an immune response ( Common)

Renominate vaccines

subunit vaccines produced by genetic modification of yeast or insects

Toxoids

inactivated toxins

Virus-like particle ( VLP) vaccines

resemble intact viruses but do not contain viral genetic material ( empty capsule heads of viruses)

Ploysaccharide vaccines

made from molecules in pathogen’s capsule ; not very immunogenic ( charbohydrate)

• Pneumococcal vaccine

conjugated vaccines

polysaccharide antigen is attached to a protein

DNA vaccines

injected naked or encapsulated DNA into muscle stimulates humoral and cellular immunity

mRNA vaccines

mRNA enclosed in a lipid nanoparticle in injected into muscle where it directs the synthesis of the encoded antigen