DR Medhat MRCP

Immune response to pathogen :
A) Innate immune response :
- When a pathogen succeedes to pass through the natural barriers e.g through
injured skin or mm, this ++ the innate immunity response as follows :
1. Recognition of pathogen-associated molecular pattern (PAMP s ) via
pattern recognition receptors (PRR S ) :
- These receptors are expressed on the surface or intracellulary in
various types of innate immunity cells .
- The most common PRR S are Toll-like receptors (TLR)
- These receptors can recognize the pathogen-associated molecular
pattern (PAM PS ) (e.g lipopolysacharide component of the outer
membrane of G-ve bacteria)and they distinguish them from self tissue
2. Binding of TLR on the surface of the mast cells & basophils to PAMP S →
Inflammatory reaction :
a) Release of histamine granules from the mast cells & basophils → VD
of local blood vessels, increase of their permeability & filtration of
inflammatory cells (neutrophils ,NK-cells & monocytes which when
they go to the tissues they differentiate into macrophages &
dendritic cells which are antigen presenting cells ,APC), these cells
through cytokine signals can recruit more & more inflammatory cells
b) Redness & swelling (i.e inflammation)
3. Opsonisation & phagocytosis of the pathogen
- By the phagocytes (neutrophils ,macrophages, dendritic cells).
- Neutrophils are the 1 st cells reaching the area of invasion by pathogen
(they are most abundant & most motile) & they phagocytose the
pathogen, degradate it & separate its surface PAMPs (= antigens) by
its lysosomal enzymes the releasing these free antigens into the tissue
fluid then to lymphatic system → to LN
- Macrophages & dendritic cells also phagocytose & lyse the pathogen
but they don`t release free antigens like neutrophils do but via
intracellular signaling the nucleus of APCs is ++ to express a specific
protein called major histocompatibility complex which fix , recognize
& lable the peptide antigen, so, via this MHC-II , the APC can present
the peptide antigen to the adaptive immunity in lymphatic system
4. Antigen presentation to the adaptive immunity
- The antigen presenting cells (dendritic cells &macrophages)
migrate to the draining LN carrying the antigen on their MHC surface
proteins & presenting it to the adaptive immunity.