2. Major Histocompatibility
Complex
The major histocompatibility complex (MHC) is a set of genes
that code for cell surface proteins essential for the acquired
immune system to recognize foreign molecules in vertebrates,
which in turn determines histocompatibility.
• Once a T-cell response has been initiated, macrophages and B
cells that have taken up specific antigen also become targets
for armed effector T cells.
• Peptides from intracellular pathogens that multiply in the
cytoplasm are carried to the cell surface by MHC class I and
MHC class II and CD4 T cells respectively.
3. Continued…
• These T cells can differentiate into two types
of effector T cells, called TH1 and TH2.
• Pathogens that accumulate in large numbers
inside macrophage and dendritic cell vesicles
tend to stimulate the differentiation of TH1
cells, whereas extracellular antigens tend to
stimulate the production of TH2 cells.
4. Antigen Presenting Cells (APCs)
• Dendritic cells
• Macrophages
• B cells
APC presents MHC class II (MHC-II) specific
for CD4 T cells while all nucleated cells have
MHC class I (MHC-I).