Pathogen Associated Molecular Patterns (PAMPs) are conserved molecules in microorganisms recognized by the innate immune system, enabling hosts to differentiate between self and non-self. Pattern Recognition Receptors (PRRs), mainly found on phagocytes, detect PAMPs and include secreted, endocytic, and signaling types, such as Toll-like receptors (TLRs). The document emphasizes the significance of these components in initiating immune responses and their role in innate immunity.

1. Mr.L. Mugala
Lesson 5
©2024
Pathogen Associated Molecular
Patterns (PAMPs)

2. Pathogen Associated Molecular Patterns (PAMPs)
 These are molecules associated with groups of
pathogens that are recognized by cells of the
innate immune system.
 These molecular patterns are conserved in
microorganisms.
 These molecular patterns are unlikely to mutate.
 These however are not expressed by host tissues.

3. PAMPs
 The absence of PAMPs on host tissues enables the host
cells to distinguish self from non- self.
 A typical PAMP is bacterial DNA.
 This DNA shows unmethylaated pairs of cytosine and
guanosine (CpG).
 LPS is the major component of the cell wall of gram
negative bacteria.
 Peptidoglycans are major components of the cell wall of
gram +ve bacteria.

4. Pattern recognition receptors(PRRs
 PRRs recognize PAMPs.
 PPRs are expressed mostly on phagocytes.
 A typical example of PRRs are Toll-like receptors(TLRs).
 TLRs are homologous to drosophila protein called Toll.
 This protein(Toll) protects insects against infection.

5. PRRs
 There are atleast ten members of the Toll family of
receptors.
 TLR4 is the receptor for Lipopolysaccharides (LPS) of
gram negative bacteria.
 TLR2 is the receptor for peptidoglycans of gram
positive bacteria.
 TLR9 is the receptor for oligonucleotides.

6. Types of PRRs
 Three types or groups;
(i) Secreted PRRs
(ii) Endocytic PRRs
(ii) Signaling PRRs

7.  Secreted PRRs
 Are opsonins that bind to microbial cell wall.
 This binding tags the bacterial cell wall for
degradation by phagocytosis or complement system.
 Best known receptor for this class is Mannose binding
lectin.

8. PRRs
 Mannose binding lectin is secreted in the liver as
an ‘acute phase’ protein.
 It recognizes carbohydrates on;
bacteria
Yeast
parasites
viruses.

9. PRRs
 MBL2 gene produces mannose-binding lectin.
 Mutation in MBL2 gene leads to mannose-binding
lectin deficiency.
 Mutation may be due to some diseases.
 Mannose-binding lectin deficiency may be inherited.
 Mannose –binding lectin deficiency leads to serious
infections like pneumonia,mengitis etc.

10.  Endocytic PRRs
 Expressed on the surface of the phagocytes.
 Mediate the uptake and transport of a pathogen to
lysosomes.
 Examples.
Mannose receptor
Scavenger receptor

11.  Signaling PRRs
 These include the members of the Toll-like family.
 These transmit signals that initiate the
transcription process.
 Transcription process may result in the secretion
of proinflammatory cytokines chemokines.

12. Summary
PAMPs are conserved on bacteria but not in human
host tissues.
PAMPs are recognized by PRRs.
PRRs are expressed on phagocytes.

13. 3 Classes of PRRs
Secreted PRRs
 Secreted by the liver and remain in blood circulation e.g.
MBL
 MBL binds onto mannose on microbes
 MBL is an opsonin that opsonizes bacteria.

14. 3 classes of PRRs- Secreted PPRs
 Oposonization is the process of tagging or coating
bacteria by opsonins such as MBL, antibody and
complements
 Oposonization facilitated bacterial destruction by
phagocytosis

15. 3 classes of PRRs
Endocytic PRRs
These are expressed on the surfaces of phagocytes
They facilitate the uptake of microbes into the cell by
endocytosis
Example mannose receptors that bind onto the mannose
residue on microbes

16. 3 classes of PRRs
Signaling PRRs
These include all members of Toll-Like Receptors (TLRs).
Found on the surfaces of phagocytes
Bind onto the microbes and send signals into the cell’s
nucleus
This initiates the genes responsible for producing
proinflammatory cytokines to undergo gene expression
Gene expression yields chemical mediators of
inflammation such as histamine.

17. PRRs PAMPs
TLR9 Bacteria l DNA
(oligonucleotides)
TLR4 Lipopolysaccharides
(LPS)
TLR2 Peptidoglycans
TLR5 Bacterial flagellin
All the above PRRs are