Infection and Immunity Flashcards
Stem cells have the capacity to produce all the B cells in our repertoire. In order to do that, the immunoglobulin genes need to?
What types don’t get through and why?
What does this allow?
Commit to a particular cell, with only one antigen binding site specificity.
B cells with an affinity to self-antigens undergo clonal deletion as a protective mechanism before they even leave the bone marrow.
This allows a large repertoir of B cells, with nearly no self-antigens
What is thymus involution and what does it tell us?
- Develops under sternum, intially large and then involutes with age
- This tells us we produce most of our T cells early on in life (whereas B cells are more consistantly made)
Describe Thymus structure
- Outer cortical layer
- Inner medullary layer
- Bone marrow stem cells come into the thymus from the bone marrow and start from the top, going through a series of changes and alterations till they reach the inner, and are then exported around the body.
Describe T cell ontogeny
- Uncommited thymocyte
- stem cell come from bone marrow that is destined to be a T cell
- Rearranges T cell receptor genes ‘TCR” (both the alpha and beta)
- now we have thymocytes that are expressing genes comitted to one lineage
- TCRaB**
- TCRaB
- both CD4 (helper) or CD8 (cytotoxic) expressed!!!
- We need to make sure these cells can recognise HLA; and therefore these cells are tested to determine this, using their T cell receptor and CD4 or CD8
- Many of them will not be able to, and these will be negatively selected against ” positive selection”
- TCRaB CD8 or CD4 :These cells can recognise HLA:
- Class 1 with CD8
- Class 2 with CD4
- these down regulate the CD4/8 they don’t need
- secondary testing to make sure they’re not reactive to self peptides “negative selection”
- Left with cells that recognise HLA but to some foreign peptide!
- Both start expressing CD3
Important points from T cell oncology and T cell receptor genes
- Development occurs in the thymus
- Multiple V, D and J exons recombine to form a V-region
- Recombination is independnt of antigen
- T cells become comitted to one V<em>a</em> and one V<em>B</em>
- Positive selection for HLA class I or II recognition (required CD8 or CD4)
- Negative Selection against strong self reactivity
We develop a repertoire unique to us!! Change HLA, you change the positive selection process, and change everything!
Warning signs of immunological deficiency?
Blood count would show?
- You will only see signs post 6 months
- Recurrent infections since year old
- Sinus infections, pneumonia, strep, etc
- There will be a Failure to thrive
Blood: not massive difference but mismatch!
- WBC: lower then normal
- Neutrophils: lower
- Lymphocytes: normal
- Monocytes: higher
Serum immunoglobulin tests of an immunodeficient individual could look like who has “Hyper IgM syndrome”
- IgM: Really high
- IgG and IgA: really low!
Peripheral blood lymphocytes
- T cells (CD3) around 87%
- Activated T cells don’t bind soluble CD40 (shows co stimulator for this is low)
- Why is there High IgM but no antigen specific IgG?*
- Why no sIgG on B cells?*
What’s Hyper IgM syndrome?
Rare condition where there is an inability to switch from IgM class to the later classes, due to a CD40 ligand mutation that stops the co-stimulation.
There is no switch so the secondary response still only has IgM!
No IgG, IgA or IgE
Microbial Factors of immunity and Infection?
- Type of organism (eg; virus, bacterium, parasite)
- Dose (degree of exposure)
- Virulence
- ROute of entry
Host Factors of immunity and infection?
- Intergrity of innate barriers
- adaptive immune competence
- HLA, Ig and TCR genes
- Previous exposure
- Other infections
What types of pathogens/antigens will we see with viral, bacterial and protozoa infections?
Viruses:
- Lytic or integrated cycle
- Capsid antigens
- Internal structural components (HLA I associated with fragments of viral proteins, shows there’s something going on!)
- Metabolic Products
Bacteria and Fungi
- Extracellular (eg; S. aureus) or intracellular (eg; M. tuberculosis)
- Structural components
- metabolic products and toxins of pathogen
Parasites
- Large (multicellular) (slower)
- Life cycle changes
- Radical changes in antigenicity; to evade the IR
Immune factors to protect us from pathogens are?
- Direct neutralisation by antibodies
- Opsonisation and phagocytosis via Fc region
- Complement-mediated effects
- HLA-restricted T cell mediated Cytotoxicity
- NK cell-mediated cytotoxicity
- also have inflammatory and immunoregulatory cyctokines
- antiviral cytokines (eg interferons)
What antibodies are effective against what antigens?
- Viruses IgA, IgG and IgM
- Toxins IgG and IgM
- Extracellular bacteria IgA, IgM and IgG
- Parasites IgE and IgA
What are cytotoxic T cells effective against pathogens
Intracellular protein antigens
- Virus infections
- tumour cells: recognise changes
- transplanted organs: if not HLA identical then could be recognised
Babies failure to thrive, recurrent infections, pneumonia, otitis media, erysipelas.
Paired with Low IgG, IgA and IgM!!
Few B cells and therefore tiny/no tonsils
What is this?
Could be X-linked agammaglobulinaemia
An inability to make antibodies
THis correlates with an increase in only bacterial infections, but not really viral infections. B-cells are not vital in controlling viral infections