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What are the differences between T cell independent and T cell dependent?

How B cell being activated?

What is the primary and secondary of B cell response?

How is the structure of plasma cell?

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There are T cell dependent and T cell independent which help in B cell activation. B cell activation occurs in the secondary lymphoid organs (SLOs), such as the spleen and lymph nodes. It produces memory cell and plasma cell by different pathway.  Memory cell will recognize the pathogen and attack it faster in second infection. Plasma cell is responsible to produce antibody like IgM and can switch to different isotypes. B cell primarily prevents pathogen expansion and early detection of pathogen.

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1. Differences between T cell depedent and T cell independent.
T cell independent antigen is often polysaccharides that contain repeating epitopes/lipopolysaccharides derived from Gram-negative microorganism and is able to stimulate B-cell directly without co-stimulation of T helper cell while T cell dependent antigen is soluble protein which require the help of T cell in order to activate B cell. In T cell independent, specific naive B cells will interact with antigen receptors and produce IgM whereas for T dependent, B cell is activated by T dependent antigens require contact dependent help delivered by the interaction between CD40 on B cells and CD40L on activated  TH cells and the activated B-cell will then clonally proliferates to produce lot of plasma cells and memory cells, which all recognize the same antigen. Isotype switching will occurs in T cell dependent while no isotype switching in T cell independent.

2. Activation of B cell
T dependent cell

Resting B cells become activated by T dependent antigen via PAMP via their toll like receptors and start to proliferate.

Protein antigens become internalized, digested and presented to T cells as peptides via MHCII.

Cognate B cell / T cell interaction provides co-stimulation to B cells via CD40, which becomes activated on B cells via CD40 ligand (CD40L) expressed on T cells.

T cells also provide cytokines to B cells that support their survival (IL-4), differentiation into plasma cells (IL-21) or class switch recombination.

T independent cell

-B cells activated by antigens by recognition and binding of a common microbial constituent to TLRs or by extensive crosslinking of BCRs to repeated epitopes on a bacterial cell. B cells activated by TI antigens go on to proliferate outside lymphoid follicles but still in Secondary Lymphoid Organs (Germinal Centres do not form), possibly undergo immunoglobulin class switching, and differentiate into short-lived plasmablasts that produce early, weak antibodies mostly of class IgM, but also some populations of long-lived plasma cells.

3. Primary B cell Response

1. Following the first exposure to a foreign antigen, a lag phase occurs in which no antibody is produced, but activated B cells are differentiating into plasma cells.

2. The amount of antibody produced is usually relatively low.

3. Over time, antibody level declines to the point where it may be undetectable.

4. The first antibody produced is mainly IgM (although small amounts of IgG are usually also produced).

Secondary B cell Response

1. If the same antigen infects the cell again in the future, an accelerated secondary or anamnestic immune response occurs. This lag phase is usually very short due to the presence of memory cells.

2. The amount of antibody produced rises to a high level.

3. Antibody level tends to remain high for longer.

4. The main type of antibody produced is IgG (although small amounts of IgM are sometimes produced).

4. Structure of plasma cell
-oval shaped
-basophilic cytoplasm
-an eccentric nucleus with heterochromatin
-contains abundant of rER with well developed Golgi apparatus

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1. Macrophage is an antigen presenting cell (APC).
2. Macrophage will be activated to engulf/phagocytize the pathogens.

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1. The mechanism for the activation of macrophage.
2. The functions of macrophage.
3. The response of the macrophage.

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1. Macrophage has 3 pathways for activation
- innate pathway
- classical pathway
- alternative pathway
2. Macrophage will be differentiated into M1 & M2 when they interact with cytokines secreted by Th1 and Th2 cell respectively.
3. Macrophage has lots of receptor on its surface that can produce immune response.
4. Macrophage function can be divided into two which are immuno and non-immuno function.
5. The immuno function are sensor of invasion, phagocytosis and inflammation.
6. Non-immuno function of macrophage are muscle regeneration and iron homeostasis.

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1. 3 signals are required for activation of T cells

2. CD 4 can be divided into T helper 1 and T helper 2.

3. CD 8 can be divided into Cytotoxic T cell.

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1. What are the 3 signals required for T cell activation.

2. What are the function and of TH 1, TH 2 and Cytotoxic T cell.

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1.  Signals required for T cell activation are antigens, co-stimulators and cytokines. First signal is antigen, where it is highly specific. It involves TCR:MHC peptide interaction. Second signal is co-stimulators, where it is able to provide amplification of signal. Example of  co-stimulators are CD28:B7 and CD40:CD40L. Third signal is cytokine. Cytokine is important for growth and differentiation factor for T cell.

2. T helper 1 promotes cell-mediated immune responses and is required for host defense against intracellular viral and bacterial pathogens. T helper 2  cells play an important role in the protection against extracellular parasites.  Cytotoxic T cell has the ability to directly kill other cells. They play a major role in host defense against viral infection, as well as infection by other intracellular pathogens that replicate in the cytoplasm of the host cell.