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B cells are lymphocyte.
They produce antibodies and memory cells.
They help to remove the foreign bodies by various kind of processes.
Examples of antibodies that is produce by B cells are IgM, IgE, IgG, IgA.

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What is the function of B cells?
What is the mechanism of B cells activation?
How the B cells response to the activation?

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We learned that the function of B cells are to secrete cytokines such as interleukine, monokine and lymphokine.
Besides, the B cells also produce many kind of antibodies that we have mentioned earlier.
Next, there are two activation mechanisms which are independent antigen and dependent antigen.
The independent antigen is basically the first infection occur. Firstly, the B cells will attach to the pathogen and internalization occur. This pathogen will be degraded into 2 types of molecule which are carbohydrate or protein and produce antibody IgM.  The antibody will kill the antigen.
When secondary infection occur, the dependent antigen take place which is it consist of protein degraded by the first infection. Isotype switching will occur where IgM will switch to IgE or IgG or IgA depends on its specificity. The peptide from the protein will be express by the MHC II on the B cells itself and will be detect by the CD4 Th cell. This CD4 Th cell will secrete cytokine that will act on the cell to be activated. Activated B cell will undergo proliferation become plasma cell and become the antibodies and memory B cells.
So, in this case, dependent antigens will cause immunological memory response as it produce memory B cells.

Next the response of the B cells towards activation.
Firstly, the neutralization will take place where it prevents the antigens from binding to the cell surface. This prevention will prevent the cell being infected by the antigens. However, the antigens are not being kill yet, so the opsonization response take place. Opsonization is the process where the antibodies will be bind to the antigens and the macrophage will come and engulf the antigens. Phagocytosis process occur and the antigen being digest. There is also complement that response toward the activation of B cells. This complement will bind to the infected cell in the plasma and causing Membrane Attack Complex (MAC). MAC will make a pore and lyse the infected cell. Furthermore, the Antigen Depending Celullar Cytotoxic (ADCC) is also a response toward the B cells activation. ADCC is actually the reaction between innate and acquire immune response because the NK cell (innate) involves in degranulation process of the specific infected cells (has the specific antibody expressing on the infected cell).

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The different between intracellular and intracellular pathway.
The important type of cytokines produced macrophage that help in the activation.
How macrophage detect the present of antigen such as the present of bacteria

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Macrophage help in tissue repair and also help to kill some pathogen such as bacteria whether extracellular or intracellular.
Macrophage produce a lot of cytokines when it activated.
The present of specific receptor will determine the reaction to occur with the macrophage.
Macrophage do a process called phagocytosis whenever it encounter some pathogen.

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Macrophage have a lot of fuctions such as phagosytosis, wound synthesis, generation of nitric oxide, inflammation and protein synthesis. For the phagocytosis, it help to engulf substances such as bacteria so that it can kill it. For the wound synthesis, the macrophage will produce and enzyme called proteases, this is for the removal of the dead tissue. It will produce a growth factor that help in inducing the wound synthesis. For the generation of nitric oxide, this substances help in killing the bacteria or viruses. For the protein synthesis, it will produce lysozyme, compliment and cytokines.

This macrophage have a PRRs receptor to bind to the PAMP present at the surface of bacteria. The PRRs have two types which is TLR 2 for positive gram bacteria anf TLR 4 for negative gram bacteria. There is also present of CD31 receptor to monitor the condition of the Neutrophil. This macrophage the will release a cytokines.

For the M1, it will produce pro-inflammatory cytokines such as IL-12 and TNFa. Both of this will react to the Th0 and NK cell. Then both of this cell will produce IFNa which will activate the macrophage. Once activate, it will cause the size, phagocytosis, Nitric Oxide production and etc to increases. For M2, it will produce anti-inflammatory cytokines which will produce IL-10, IL13 and IL-4. This cytokines will compete between IFNa at the macrophage receptor. This cytokines will suppressed the IFNa. It also can cause the Th0 to become Th2 which will react with B cell to become plasma cell and produce antibody.

For the extracellular part, the macrophage will undergo process called phagocytosis. There is four stages which is chemotaxis, adherence, ingestion and digestion. Once the marophage engulf the bacteria, it will  produce phagosome. Then it will react together with lysosome and  become phagolysosome. The the protein of the bacteria will become peptide. The peptide will the go the MCH class ii at the endoplatic reticulum. Then it will go to the outer part to become APC. The naive CD 4 T cell will detect the present of the receptor and react with it. This will cause the CD4 T cell will become activated.
For the intracellular, the bacteria will bind to receptor present in the macrophage such as TLR7. The it will produce autophagosome. This will become autophagolysosome once bind to the lysosome. There are two types of reaction which depends on the oxygen dependent or non oxygen dependent. For the oxygen dependent, the arginine will produce nitric oxide with the present of NADH and nitric oxide synthase. It will produce nitric oxide. But will react with oxygen to produce nitric dioxide which is help to kill the bacteria effectively. For the non oxygen dependent, the argine will become ornithine by the arginase enzyme.This will help to kill the bacteria.The macrophage will produce cytokines which will react with lymphocyte such as NK cell which will help in the removal of the bacteria.

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T Cell                                            

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T Cell                                            

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T cell is activated through 3 signal which are antigen, co-stimulation and cytokines. For the signal 1 which is antigen, it is differentiated according to where the antigen located. If the antigen is located extracellular, the macrophage will phagocytised the extracellular antigen until it become peptide. Then, the peptide will bind to MHC class 2 and will presented to surface (APC) of the macrophage then will further bind with CD4+ T-cell. While if the pathogen located intracellular, the antigen will be presented by MHC class 1 which will further bind to CD8+ T-cell.

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Then, we moved to signal 2 which is co-stimulation. When the macrophage detect the pathogen, it will express co-stimulators which are CD40 and B7. This co stimulators will bind with T-cell where the co-stimulator CD40 will bind to CD40 ligand and B7 will bind to CD28.

The last signal is cytokines. The binding of TCR and MHC antigen complex will make the macrophage release the cytokines. The most important cytokines that be released here is IL-2. These cytokines will proliferate T-cell.

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Besides, we will focus on the response of the T-cell. It is according to CD4 and CD8 T-cell. For CD4, the T-cell is activated when the peptide of the antigen is presented by the MHC class 2. The CD4 will secrete IL-12 to turn naïve T-cell into Th1 and further will make Th1 secrete IFN-y and IL-2 which functioning in regulating immunological activity of the macrophages. Beside that, the CD4 will secrete IL-4  to Th2 and further make the Th2 secrete IL4, IL5, IL10 in order to make B-cells proliferate into plasma cell which functioning to secrete antibody and undergo humoral immunity.

For the CD8 T-cell, it is activated when the antigen peptide is present by the MHC class 1. T-cell will secrete cytokines (TNF-a and IFN-y) which have anti inflammatory and anti-viral microbial effects. Besides, production and release of cytotoxic granules also found in NK cell which are perforin for infected cell lysis and granzymes for shutting down the viral proteins and apoptosis.