Lecture 19 Immunology and Pathogenicity and Infection Flashcards
What is the major mechanism that involves the rearrangement of antibody gene segments
VDJ Recombination
Describe VDJ Recombination
- Recombination Activating Gene (RAG) enzymes
- Activated in B cells
- Randomly cut and paste gene segments.
When does Random Rearrangement of antibody gene segments occur?
- As B cells develop in the bone marrow
- Early in embryonic life, before infection
What is tolerance?
Removal of self-reactive B cells
Largely occurs in bone marrow
What happens to the B cell upon infection?
- antigen “selects” B cell with antibody that matches it.
- B cell proliferates, forming clone of identical cells, each with antibody for the antigen.
Secondary Response to antigen.
Activation of memory B cell strong response
- Basis of Immunization
Humoral
B cell and production of antibodies
- extracellular pathogens
Cell - Mediated
- intracellular pathogens
- T cell
T cells
- Originate in bone marrow, mature in thymus
- Activated when their receptors bind antigens presented by other cells
Helper T cells
-Make cytokines, activate B cells, macrophages, or other T cells
Cytotoxic T cells
- kill cells expressing foreign antigens using
Perforins and Granzymes (enzymes)
What are the enzymes that Cytotoxic T cells use and what is there function?
Perforins - form pores
Granzymes - induce apoptosis
Describe Cluster of Differentiation (CD) molecules and the common examples.
- membrane proteins on immune cells
- Call also be used to determine cell’s identity
- Helper T cells - CD4
- Cytotoxic T cells - CD8
T - Cell Receptors (TCRs)
- Receptors bind antigens (usually peptides) presented to the, by other cells
- Only when presented with a MHC molecule
- TCRs are expressed from gene segments rearranged in thymus.
Human Leukocyte Antigen (HLA)
- Humans have 2 sets of MHC genes
- One from each parent both are expressed
-Closer 2 people related, more similar their HLAs, important in donor selection for tissue, bone marrow and organ transplant- HLA Typing.
Class 1 MHC
- on all nucleated cells
- present peptides that originate in cytoplasm from intracellular pathogens
- Present peptides to CD8+ Cytotoxic T cells
Class 2 MHC
- only on antigen-presenting cells (dendritic cells, macrophages, B cells)
- Present peptides from extracellular pathogens, taken up by phagocytosis
- Present peptides to CD4+ Helper T Cells
What is a Pathogen
- Organism that produces disease
Opportunistic Pathogen
-Infects host with weakened immune system
Carrier
-Infected individual potential source of infection (no observable symptoms)
Zoonoses
-diseases transmitted to humans from animals
Vector
-Organisms (usually insects) that transmit disease to humans - mosquitoes, ticks, fleas
Pathogenicity
ability to produce disease
Virulence
degree of pathogenicity
Latency
Pathogen stops reproducing, dormant, can become active again
How do we measure virulence?
- Lethal Dose 50 (LD50)
- # to kill 50% of hosts
- Infectious Dose 50 (ID50)
- # of pathogens required to cause clinical disease in 50% of inoculated hosts
How do we study pathogens, Virulence and Pathogenicity.?
Model Systems - animal models, cell culture
Human Studies - Clinical Trials, Case studies
Epidemiology - Examine incidence, distribution, control of disease
