Acquired Immune System

B Cells

• 2 light and two heavy chains

•  Disulfide bonded (intra and inter)

• Bispecific (Bivalent)
• Biological function lies within the C region

• Ab research really opened up in the 1970’s
• Blood sample from patient that could not urinate was taken and tested
• A discrete Ab was seen in the blood

• Patient had the ability to make only one Ab (IgG)

• Condition was due to multiple myeloma (cancer of the plasma cells)

5 Classes of Ig's

1. IgG

2. IgA

3. IgE

4. IgM

5. IgD

What is the most abundant Ig in the body.  ( it can cross the placenta)

Which Ab is present in mother's milk?

Antigens-Immunogens

Antigenic Determinants (Epitopes)

B-lymphocytes have B-cell receptors (BCRs) corresponding to the specific antibody molecule they are genetically programmed to make. These BCRs recognize epitopes of antigens having a complementary shape. Different B-lymphocytes are programmed to produce different BCRs, each specific for a unique epitope.

Polyclonal vs monoclonal Antibodies

• Polyclonal response made up of monoclonal Abs

• We mount a polyclonal response during the IRS

Typical Immune Response

• Polio
• Initial response started out by IgM
• IgG activated later
• IgG most prevalent Ig in body
• 

Low Response

• IgM response.

• T cell independent

Taking a closer look at cell involvement.

Clonal Expansion

High Response

• T cell dependent

• IgG now becomes involved

How do T cells get involved in the IRS?

T- Cells

T helper 1 and 2

T cytotoxic - killer T

In order for a T cell to get involved in the IRS, it needs to be presented the antigen in a very specific manner.

This is made possible via presentation of the antigen by an Antigen Presenting Cell (APC)

• Macrophages (MO)

• C cells

• Dendritic cells

Key Players in T cell dependent Response

• MHC

• TCR

• APC

MHC

·                    We know that transplants are rejected in a timely fashion (2 weeks)

·                     Blood transfusions are difficult

Why is this the case?

·                     Due to differences in the MHC

·                     MHC = glycoproteins that are embedded in the plasma membrane of cells and act as biochemical fingerprints unique to and individual.
Are highly polymorphic (genetically different)

Sequence of Events

• Ag recognized by Ab on B cell

• Ingested by B cell (APC), immunogen broken down

• Select peptides of immunogen presented on surface of B cell via MHC (B cell is now acting as an antigen presenting cell. APC)

• Peptide is presented to T helper cell via TCR.

• Cytokine release (chemical signals)

• Cytokine release from T helper cell telling B cell to continue making Ab's that are specific to the immunogen.

MHC Restriction

• Compared to B cell receptors, TCR’s are membrane bound and do not appear in the soluble form
• TCR’s are not only specific not for the antigen alone but for antigen combined with the MHC

T_H cells are activated and proliferate only when presented with the antigen via self MHC.

Why is this a good idea?  Think about the roles that Tc and Th play.

NK cells

• Neither T or B cells
• May be lymphoid in origin
• Has no surface markers typical of T cells or B cells
• It marker is CD16
• Have ability to kill tumor cells

Q. How do NK cells recognize tumor cells?

1. Can detect differences in lipid composition of tumor cells
2. Look at profile of receptors that the altered cell is expressing

 Q. What does this suggest about tumor cell receptors?

Differences between tumor and normal cells

• Tumor cells are likely to down regulate class I receptor
• Therefore Tc has difficulty recognizing altered cell

Defects in the IRS

Nude & SCID mice

In a nude mouse why was there a low response as opposed to no response at all?

What would have a larger effect on immune response, thymectomy or bursectomy?