3. B lymphocyte Clonal Selection Process
Plasma Cells

5. In cell mediated immunity, the B cell which make the
Ab’s which are part of the humoral immune system. There are also other
lymphocytes known as the T cells
T cells have different subtypes based on cell surface proteins they express
which are given the names of CD (cluster determinant or differentiation)
T cells expressing certain CD’s are designated as CD (#) +
Two major types of T cells based on their CD’s are:
CD 8 +  cytotoxic T cells, ATTACK
CD 4 +  helper T cells, secrete chemical messengers that
are called lymphokines, which regulate the immune
response, HIV wipes these guys out

8. The combination of antigen and MHC will then be recognized by
the T cell.

10. Cytotoxic T cell Helper T cell
Antigen Presenting
Cell (APC)

14. antigen

15. CD 4+ Helper T Cell

19. Complement are serum proteins which are very active biologically and have the
ability when activated to lyse cells or microbes
- synthesized in the liver, macrophages, monocytes, intestinal
epithelial cells
- act in concert as a cascade like the coagulation process
- have no memory so have no effect on immunity
Two complement pathways:
- classical, which requires Ab-Ag to initiate
- alternative, initiated by binding of complement proteins to the
cell membrane of the invader

20. Ab-Ag initiates
Membrane attack complex

21. Activation of C1, which consists of 3 subgroups called C1q, C1r, C1s
- C1q binds to a C1q specific receptor on the Fc region of at
least two adjacent Ig molecules or a single IgM
- C1q then becomes activated and activates C1r and C1s
- C1 then activates C4
C4 when activated then binds to the cell membrane near the Ab-Ag complex

22. Classical pathway

25. Many of the complement components and fragments
also possess biological activity
- C3b enhances phagocytosis by macrophages and neutrophils
- C3a, C4a, C5a activate mast cells and basophils
- C5a is also a chemoattractant for neutrophils and macrophages
- these link up the processes of inflammation/infection with
the complement system

26. Now suppose we want to transplant therapeutic cells into a patient to
correct some type of condition
- immune system very good at recognizing self and non-self
- immune response to foreign cells involves a combination of Ab,
complement activation, macrophages, B and T cells
Ab recognizes the foreign antigens presented by the transplanted cells and
induces the destruction of the transplanted cells by activation of complement
and NK cells by ADCC (Ab dependent cell-mediated cytotoxicity)
- there is also a T cell response against the MHC molecules present
on the transplanted cells which contains foreign MHC class I and
MHC class II molecules (these latter as passenger leukocytes
and macrophages present in the transplanted tissue)

28. Sometimes immunity rather than protecting can cause damage or even death
Called hypersensitivity reactions leading to exaggerated or inappropriate
Immune responses
Divided into 4 classes, as types I – IV
Type I: anaphylactic reactions, mediated by IgE Ab’s which bind to receptors
on mast cells, when crosslinked by antigens, the IgE Ab’s trigger
the release by the mast cells of very active agents like histamine,
leading to symptoms of anaphylaxis (which means
“away from protection”), happens in minutes
Mast cell
Type I hypersensitivity

31. Type II: cytolytic or cytotoxic reactions occur when IgM or IgG bind to antigen
on the surfaces of cells and activate the complement system which
destroys the cells by formation of MAC
Type III: immune complex reactions, complexes of antigen and IgM or IgG
accumulate in the circulation or in tissue and activate complement,
granulocytes are attracted to the sites and damage the tissue
Type IV: cell-mediated immunity reaction, or delayed hypersensitivity, is caused
by T cells rather than by Ab’s, the activated T cells release lymphokines
that cause the activation and accumulation of macrophages which
cause local damage. Has a delayed onset of 1-2 days.

35. Progression
Wheal and flare, localized
- wheal  increase in vascular permeability causes swelling
- flare  blood vessel dilation causes redness
2. Systemic reaction much more severe
- difficulty in breathing due to constriction of bronchiolar muscles
- increase in vascular permeability results in loss of fluid from blood
into the tissue spaces (hives and edema) which can lead to drastic
fall in blood pressure and shock which is known as anaphylactic shock,
give epinephrine which reverses the effects of histamine by relaxing
smooth muscles and decreasing vascular permeability