section 35.1
Innate immunity
807
TABLE 35-1
Components o f the Immune System (continued)
Protein Components
Principal Functions
Comments
Related
Figure(s) or
Tables
Complement
Plasma proteins that act
sequentially to produce cell
lysis, facilitate phagocytosis
Table 35-3
Classical pathway
Creates the proteolytic enzyme
complex, C3 convertase
(C4b2b)
Initiated by interaction with
antigen-antibody complexes
Figure 21
Alternative pathway
Creates the proteolytic enzyme
Initiated by reaction of the C3
Figure 21
(Properdin pathway)
complex, C3 convertase
(C3bBb)
thioester with nucleophilic
molecules on cell surfaces
Lectin pathway
Recognizes mannose in
oligosaccharide chains
Initiated by binding of mannose
binding protein to foreign cell
carbohydrate residues
Figure 21
C3 Convertase
Principal agent responsible for
reactions that lead to formation
of the membrane attack
complex and lysis of the
invading cells
NOTE: Two different C3
convertases are formed by the
classical and alternative
pathways
Figure 21
Opsonins
C3b, C5b, the mannose-binding
protein, CRP (C-reactive
protein) are examples of
opsonins
Proteins that adhere to microbe
surfaces making them
“attractive” for attack by
complement and phagocytes
Antigen Presenting
Proteins that display peptide
Human leukocyte antigens
Figures 1, 2,
Proteins
fragments of foreign (nonself)
Class I:
HLA-A, HLA-B,
and 3
(MHC proteins)
proteins on the surface of cells
HLA-C
Class II:
HLA-DP, HLA-DR,
HLA-DQ
Class I MHC
Present on all nucleated cells,
Structure:
Figure 3
HLA-A,
present peptides to
CD
8
a
-polypeptide chain, 3
Figures 13
HLA-B,
cytotoxic T-lymphocytes
domains,
a v a 2, a
3
and
fi
2
and 14
HLA-C
(CTLs, Tc), presents
endogenously
synthesized
peptides (e.g. virus coded
peptides)
microglobulin (Not a
MHC protein)
High degree of sequence
variability in ocl and
« 2
domains
Class II MHC
Present on macrophages and
Structure:
Figures 2
HLA-DP, HLA-DR,
B-cells, presents peptides
a/3-poly pep tide chain,
2
and 3
HLA-DQ
from processed
exogenous
or vacuolar antigens for
recognition by
CD4,
Th-cells
domains,
ocv j
5
l
and
a
2
j3
2
Variability in both
a
and
/3 chains
Figure 15
j32-microglobulin
Not MHC gene coded, but
is a part of the MHC class I
antigen processing complex
Figure 14
Figure 15
