4. Humoral immunity:
Mediated by antibodies that produced from B-cells.
B- cell
- B cells or B lymphocytes are a type of lymphocyte in the humoral immunity of
the adaptive immunity
- B cells can be distinguished from other lymphocytes, such as T cells and Natural killer
cells (NK cells), by the presence of a protein on the B cell's outer surface known as a B
cell receptor (BCR).
- This specialized receptor proteins allows a B cell to bind to a specific antigen.
- In birds, B cells mature in the bursa of Fabricius. In mammals, immature B cells are
formed in the bone marrow
5. B cell maturation, activation and differentiation:
- B cell mark the antigen for destruction, where the marker that placed by B-cell
alert complement system to attack this antigen
- B cell possess BCR binds with Ag direct without aid of MHC as in TCR.
6. - BCR consists of:
a) Ligand Binding moiety:
- membrane bounded immunoglobulin with integral
membrane protein - Y shape
- Encoded by Ig genes (V,D,J DNA segments by DNA
rearrangement) - V,D,J segments encodes heavy chain
- V, J segment encode light chain
b) Co-stimulating molecules = CD79= signal transduction
molecule: once BCR binds to Ag, CD79 activated and send
signals to induce expression of cytokines stimulate the
differentiation of B cells
7. The binding of Ag with BCR, activate CD79 to send signals that induce:
1) Class switching: mutation in Ig genes of constant region to activate B
cell to produce different classes of Abs
2) Somatic hyper-mutation: adaptation of immune system to recognize Ag
by promoting mutation of variable region of Ig genes to increase affinity of
Ag-Ab binding
Also, somatic hyper-mutation induce affinity maturation “ process by
which B-cell produce Ab with high affinity to Ag during immune response”
9. - Antibodies are glycoproteins, which are sensitized, and secreted by
plasma cells in response to specific antigenic stimulation and it forms
about 20% of plasma protein
- Antibodies can be found in blood plasma or serum and in many body
fluids such as tears, saliva.
Complete antibody Incomplete antibody
- Heat resistant
- They will produce different immunologic
reaction
- Passing the placental barrier.
- Heat labile substances
- Do not show any immunologic reaction
when they bind with an antigen.
- Not able to cross the placental barrier.
- There are two types of antibodies: complete and incomplete antibodies.
10. Digestion of IgG with papain ( protease enzyme) produces two types of fragment:
1- Fraction antigen binding= Fab
- This is the highly variable area which determines
specificity
- consisting of the light chain and two domains of
the heavy chain (denoted VH and CH1)
2. Fraction crystalline Fc
which determines what happens once the Ab-Ag
interaction has occurred. Consisting of the
remainder of the heavy chain (CH2 and CH3).
- It is a complementary binding site.
