Immune Response to Viral Infections Flashcards
Host-virus relationship
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
Non-specific response to viral infection
- 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!*
Specific response to viral infection
Humoral
- immunoglobulins
- neutralize virus infectivity
- elimination of infectious virus
- mediated by plasma cells (B lymphocytes)
Antigen
Molecule which induces the formation of antibody
- protein and carbohydrate
Epitope
Single antigenic determinant as a smallest unit of antigen
Antibody
Molecule produced by animals in response to antigen
Humoral
B lymphocytes respond to an antigenic stimulus by producing and secreting specific immunoglobulins (antibodies)
Cell mediated
Responds to an antigenic stimulus by the activation of several kinds of T cells and the production and secretion of lymphokines
What happens when the immune system goes wrong?
- tissue damage in vital organs
- virus evades the immune system and establishes a persistent infection
IgM
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!!
IgG
Formed later than IgM
- persists for months or years
- responsible for immunity against reinfection
IgA
Dimer of 2 IgG moleucles
- found in body secretions
- important resistance to infection of the respiratory, urogenital, and intestinal tracts
- not routinely measured
Cellular immune response
Elimination of virus infected cells
- mediated by T cells, macrophages, neutrophils, cytokines
Th
T helper cells
- stimulate cytotoxic cellular response and activate B cells
Ts
T suppressor cells
- control and regulate the cytotoxic cellular response by suppressing Th cells
Tc
Cytotoxic T cells
- main effector cells which kill virus-infected target cells
Td
Delayed hypersensitivity T cells
- release macrophage activation factor
NK
Natural killer cells
- direct killing of virus-infected cells
- no memory, no MHC restriction and no dependence on antibody
Interleukin
IL-2, IL-1
- modulate immune response
Antigen presenting cells
Variety of cell types which carry antigen in a form that can stimulate lymphocytes
- monocytes/macrophages
- dendritic cells
Major histocompatibility complex
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
Artificial passive immunization
Injection of antibodies that can temporarily protect against infection
- ex: canine distemper, feline panleuk, hog cholera
Natural passive immunity
Transfer of maternal antibody from dam to fetus
Transfer of maternal antibodies
- 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
Viral vaccines
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
Live (attenuated) vaccines
Replicates in the host, induce a lasting response without causing disease
- produce a subclinical infection
Administration routes
- subcutaneous
- intramuscular
- oral
- aerosol
- eye drop
- drinking water (for poultry)
Vacca
Cow
- 1798 used cowpox to control human smallpox
- produces a mild lesion in humans and is antigenically related to smallpox
Virulent viruses used as vaccines
Given by an unnatural route
- wild type infectious laryngotracheitis virus given by blushing cloaca
- produces minimal disease but induces good immunity
Attenuated live virus vaccines
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
Virus vectored vaccines
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
Inactivated vaccines
Made from virulent virus and use chemical or physical agents to destroy infectivity while maintaining immunogenicity
Virus subunit vaccines
Produces large amounts of viral protein by recombinant DNA technology
