Immune Response to Viral Infections

Question 1

Host-virus relationship

Answer 1

Interaction between host and virus affecting development and outcome of an infection

• hosts primary physical barriers
• host’s immunologic ability to control and eliminate the invading virus
• viral ability to evade destruction
• ability of virus to spread in the body

Question 2

Non-specific response to viral infection

Answer 2

• skin: intact, impermeable barrier
• respiratory: cilia, mucous
• GI: acid, lymphoid tissue
• urinary: flushing effect of urine flow
• conjunctiva: tears
• phagocytosis: neutrophils, macrophages
• interferons: help overcome virus infections
• no memory!*

Question 3

Specific response to viral infection

Answer 3

Humoral

• immunoglobulins
• neutralize virus infectivity
• elimination of infectious virus
• mediated by plasma cells (B lymphocytes)

Question 4

Antigen

Answer 4

Molecule which induces the formation of antibody

- protein and carbohydrate

Question 5

Epitope

Answer 5

Single antigenic determinant as a smallest unit of antigen

Question 6

Antibody

Answer 6

Molecule produced by animals in response to antigen

Question 7

Humoral

Answer 7

B lymphocytes respond to an antigenic stimulus by producing and secreting specific immunoglobulins (antibodies)

Question 8

Cell mediated

Answer 8

Responds to an antigenic stimulus by the activation of several kinds of T cells and the production and secretion of lymphokines

Question 9

What happens when the immune system goes wrong?

Answer 9

• tissue damage in vital organs

- virus evades the immune system and establishes a persistent infection

Question 10

IgM

Answer 10

Earliest antibody produced

• pentamer of 5 IgG molecules
• formed after a week of infection
• persists for 4-6 weeks
• does not cross placenta in any species!!

Question 11

IgG

Answer 11

Formed later than IgM

• persists for months or years
• responsible for immunity against reinfection

Question 12

IgA

Answer 12

Dimer of 2 IgG moleucles

• found in body secretions
• important resistance to infection of the respiratory, urogenital, and intestinal tracts
• not routinely measured

Question 13

Cellular immune response

Answer 13

Elimination of virus infected cells

- mediated by T cells, macrophages, neutrophils, cytokines

Question 14

Th

Answer 14

T helper cells

- stimulate cytotoxic cellular response and activate B cells

Question 15

Ts

Answer 15

T suppressor cells

- control and regulate the cytotoxic cellular response by suppressing Th cells

Question 16

Tc

Answer 16

Cytotoxic T cells

- main effector cells which kill virus-infected target cells

Question 17

Td

Answer 17

Delayed hypersensitivity T cells

- release macrophage activation factor

Question 18

NK

Answer 18

Natural killer cells

• direct killing of virus-infected cells
• no memory, no MHC restriction and no dependence on antibody

Question 19

Interleukin

Answer 19

IL-2, IL-1

- modulate immune response

Question 20

Antigen presenting cells

Answer 20

Variety of cell types which carry antigen in a form that can stimulate lymphocytes

• monocytes/macrophages
• dendritic cells

Question 21

Major histocompatibility complex

Answer 21

Genetic locus encoding MHC class 1 and 2 proteins

• class 1: glycoprotein found in plasma membrane of most cell types
• class 2: glycoprotein confined to APCs

Question 22

Artificial passive immunization

Answer 22

Injection of antibodies that can temporarily protect against infection
- ex: canine distemper, feline panleuk, hog cholera

Question 23

Natural passive immunity

Answer 23

Transfer of maternal antibody from dam to fetus

Question 24

Transfer of maternal antibodies

Answer 24

• IgG can cross placenta, but not IgM
• placenta of most domestic animals (ruminants, horses) is more complex and acts as a barrier to IgG
• postnatal transfer (colostrum) is more important for domestic animals
• maternal antibody affects vaccination schedules

Question 25

Viral vaccines

Answer 25

Immunization is most applicable way of preventing viral disease

• some differences between immunization practices in humans and animals
• vaccine-associated illnesses are less tolerated than in animals
• cost

Question 26

Live (attenuated) vaccines

Answer 26

Replicates in the host, induce a lasting response without causing disease
- produce a subclinical infection

Question 27

Administration routes

Answer 27

• subcutaneous
• intramuscular
• oral
• aerosol
• eye drop
• drinking water (for poultry)

Question 28

Vacca

Answer 28

Cow

• 1798 used cowpox to control human smallpox
• produces a mild lesion in humans and is antigenically related to smallpox

Question 29

Virulent viruses used as vaccines

Answer 29

Given by an unnatural route

• wild type infectious laryngotracheitis virus given by blushing cloaca
• produces minimal disease but induces good immunity

Question 30

Attenuated live virus vaccines

Answer 30

Obtained by serial passage through cell cultures, lab animals, or embryonic eggs

• select temperature sensitive mutants
• construct deletion mutants by genetic engineering –> excise gene that is not essential for viral replication, but contributes to virulence

Question 31

Virus vectored vaccines

Answer 31

Uses viruses as vectors to carry the genes for the protective antigens of other viruses

• fowlpox, adenoviruses, herpeviruses
• vaccina: rabies constructs used for vaccination of foxes and raccoons

Question 32

Inactivated vaccines

Answer 32

Made from virulent virus and use chemical or physical agents to destroy infectivity while maintaining immunogenicity

Question 33

Virus subunit vaccines

Answer 33

Produces large amounts of viral protein by recombinant DNA technology