Immune Response to Pathogens

Question 1

name the humoral immunity responses to viruses

Answer 1

• antibody: neutralization; antibody-dependent cell-mediated cytotoxicity (ADCC) and complement activation
• interferon (alpha and beta): produced by virally infected cells
  
  • inhibit transcription and translation in neighbor cells
• IFN-gamma: activates macrophages and NK cells and enhance adaptive immune system upregulating expression of MHC class I and II

Question 2

name viral strategies to avoid immunity

Answer 2

• antigenic shift and drift (e.g. influenza): mechanism of antigenic variation
• polymorphism (e.g. adenovirus, rhinovirus): circumvents immunologic memory by expressing different immunologic targets
• latent virus (e.g. herpes simplex virus, varicella-zoster)
• modulation of MHC expression (e.g. adenovirus, EBV, CMV, HSV, VZV)
• infection of lymphocytes and their death (e.g. HIV, measles, CMV)
• prevention of complement activation

Question 3

describe orthomyxoviruses (influenza)

Answer 3

• 3 distinct influenza virus type: A, B, C; type A causes infxns
• viral infection:
  
  • virus attaches to and multiplies in the cells of the respiratory tract
  • segments of RNA genome enter the nucleus (transcribed/translated)
  • finished viruses are assembled and budded off the cell with an envelope

Question 4

describe the influenza virus cycle

Answer 4

Question 5

describe the glycoprotein spikes on influenza viruses

Answer 5

• hemagluttinin (H): 15 different subtypes; most important virulence factor; binds to host cells
• neuraminidase (N): 9 subtypes - hydrolyzes mucus and assists viral budding and release

Question 6

contrast antigenic drift and antigenic shift

Answer 6

• constant mutation is called antigenic drift–gradually change their amino acid composition
• antigenic shift–one of the genes or RNA strands is substituted with a gene or strand from another influenza virus from a different animal host
  
  • genome of virus consists of 10 genes encoded on 8 separate RNA strands

Question 7

describe cell-mediated immunity with bacteria

Answer 7

• phagocytic cells kill most bacteria
• helper T cell is required for the generation of the antibody response (Th2 help)
• B-cells can recognize protein and non-protein antigens

Question 8

describe the humoral immunity response to extra-cellular bacteria

Answer 8

• complement: activated via the lectin or alternative pathway
  
  • C3b: opsonin
  • C3a and C5a: recruit leukocytes
  • MAC: perforate outer lipid bilayer of G-ve bacteria
• lysozyme: antibacterial that attacks NAM-NAG links (peptidoglycan) in the bacterial cell wall which result in lysis
• antibody: principal defense against extracellular bacteria
  
  • neutralization
  • activation of complement
  • opsonization

Question 9

describe bacterial strategies to avoid immunity

Answer 9

Question 10

describe the immune response to protozoal infections

Answer 10

• protozoa are microscopic; single-celled organisms
• protozoa cause intracellular infection, have marked antigenic variation and are often immunosuppressive
• they have complex life cycles, with several different stages and therefore present the immune system with a variety of challenges
• protozoal infection is often chronic since the immune system is not very efficient at dealing with these organisms
• most of the pathology of protozoal disease is caused by the immune response

Question 11

describe the immune response to fungi

Answer 11

• innate immunity controls most fungal infections
  
  • phagocytosis by neutrophils is a strong defense against most fungi
  • the alternative and lectin pathways of complement activation are triggered by components present in most fungal cell walls

Question 12

which cytokine is involved in fungal immunity?

Answer 12

IL-17

defective Th17 cell differentiation has been linked to recurrent filamentous fungi and the occurrence of mucocutaneous candidiasis in patients with primary immunodeficiencies