Question

Question 1: How do T helper cells participate in B cell activation? Why might a second signal act as a safety mechanism to protect the host?

Question 2: What role does the lymphatic system play in the adaptive immune system?

Answer 1

Answer 1: The answer is attached below:

Role of Th cells in B-cell activation :- Two signals are required for proper activation B-cells. [signal I signal I is generated by Antigen cross linking ding of antigen to antibodies present on surface of B-cells) which leads to the increased expression of class:IMHC and co-stimulatory B7. The antigen - antibody complex is internalized by receptor -mediated endocytosis and degraded to peptides which bind to class- I MHC and presen B-cell membrane as beptide-MHC complex. This complex (MHC-E-peptide) is refognized by The cell. This interaction activates TH cell. . (signal 2 is generated them by interaction of CD40 (present on B-cell membrane) and CD 40L/present on The cell membrane). for B-cell activation. * A costimulatory signal is also provided by interaction between B7 18-cell membrane) and CD28 ( of Th-cell membrane). In presence of all the above signals, B-cell begins to express receptors for various cytokines released from The cello Binding of cytokines support B-cell differentiation.

Antigen " signatı (MHC I(MHC-TI-Antigen - TeR) comblon Nucleus! Nucleus TER=T-cell receptor Antigen internaterted MHC-ma- TER Jeda and degraded into peptides a B7 C0281 co-stimulatory signal como [CDuod Nucleus signal - T-cell B-cell .

* The second signal acts as safety mechanism to protect the host because it leads to the activation and differentiation of B-cells into antibody secreting plasma cells and memory B-cells me The memory B-cells persists int the body for long-time secreting antibodies. So, if the same antigen % encountered second time or so, these memory B-cells responds immediately and kill the antigen.
Answer 2: Lymphatic system plays an important role in adaptive immune system. It includes lymph vessels, lymphocytes and lymphatic organs.

Lymphatic organs include the bone marrow, thymus, lymph nodes and spleen. Bone marrow and thymus are called primary lymphoid organs which participate in immune response. Bone marrow contains tissue that produces lymphocytes ( B- and T- lymphocytes) which are known as the cells of adaptive immune sysytem. B-lymphocytes (B-cells) mature in the bone marrow. T-lymphocytes (T-cells) mature in the thymus gland. Other blood cells such as monocytes, leukocytes and dendritic cells are also produced in the bone marrow.

Spleen and lymph nodes are the secondary lymphoid organs. Lymph nodes are found in various regions throughout the body and are highly efficient in trapping antigens which enter the body through the lymphatic vessels. These are the areas of concentrated lymphocytes, macrophages and dendritic cells along the lymphatic veins. After antigenic stimulation, the lymphoid follicles enlarge with dense population of antibody producing B- lymphocytes. Antigens are brought into these areas with the help of antigen presenting cells like dendritic cells, macrophages, etc. and presented to T- lymphocytes. all these interactions finally bring about the immune response.

The spleen is also highly efficient in trapping foreign substances that are carried in blood.If spleen is damaged or removed, the individual becomes more susceptible to infections. It is similar to lymph nodes but is larger and filled with blood. Spleen is the major organ where antibodies are synthesied and released into circulation from there. Spleen is copartmentalised into red pulp (where od RBCs are destroyed and removed) and white pulp (which is T- lymphocyte rich region). The marginal zone of white pulp is rich in lymphocytes and macrophages.