Question

30. Newly matured T and B cells that have been released to the periphery are called “naïve”

What does that mean? (2pts)

31. What is the role of CD4+ T cells? What do they do? How do we know they’re important? (2pts)

32. There are many different subtypes of CD4+ T cells. What determines what subtype they will become? (2pts)

33. What is the role of CD8+ T cells? What do they do? (2pts)

34. What is the role of T regulatory cells? How do we know they’re important? (2pts)

35. How are memory T cells different from effector T cells? (2pts)

36. Briefly describe the stages of building a BCR. (2pts)

37. Why do B cells only have to go through negative selection? (2pts)

38. What is the difference between a B-1 B cell and a B-2 B cell? (2pts)

39. What is required during T-dependent B cell activation? (2pts)

40. What is required for T -independent activation to take place? (2pts)

41. What is somatic hypermutation? (2pts)

42. What is class-switch recombination? (2pts)

Answer 1

30 ). Naive literally means without an experience. The T and B cells are called naive cells because they have been recently matured from bone marrow and thymus and they are still not exposed to antigen and not functioning. If a naive B cell gets exposed to antigen for first time then eventually it becomes memory cell or plasma cell which produce antibody , same happens in case of T cells they are activated to helper cells or cytotoxic cells after the naive T cells gets exposed to antigen .

31). CD4 t cells are also called helper T cells . Their main role is activation of other T and B cells by releasing cytokines in the circulation . Their normal range is 500 to 1500 / cu .mm .when this count is low the person is prone to secondary bacterial , viral and fungal infections . There are 2 type of t helper cells , Th1 cells are involved in cellular immunity , they secrete 2 substances interlukin 2 , these activate other t cells and gamma interferon which plays a significant role in enhancing activity of phagocytes and other natural killler cells . Th2 cells secretes interlukin 4 and 5 and activates humoral immunity by activating B cells and its production of antibodies.  

32). The antigen presenting cell ( APC ) with with class 2 mhc molecules makes interaction with naive T cells wich starts to proliferate, the T helper cells can proliferate into Th1 cells or Th2 cells , it is mainly dependent on the cytokines released from APC cells , if APC cell releases interlukin 12 and interferon gamma the t cells differentiate into th1 cells , if the APC cells release interlukin 4 the T helper cells differentiate into th2 cells .

33). Antigens with class 1 MHC molecule present to the cytotoxic T cells also called CD8 cells . They are activated by helper t cells and the antigen gets attached to the receptor in the CD 8 cells and the CD8 cells expand by taking the antigen into it and they release cytotoxic substances like lysosomal ezymes wich destroys the antigen . The virus infected cells and cancer cells in the body are initially destroyed by CD 8 tcells .

34). T regulatory cells , they are also called as suppressor cells which suppresses the activity of helper T cells and killer T cells in the body , it is essential because it prevents our body ' s own tissue by being destroyed by helper and killer T cells .

35). Some groul of naive T cells gets activated into memory t cells , they deviate from function of other effector t cells in the fact that , they will not enter the circulation instead they migrate to the other lymphoid tissues in body . When the antigen is exposed for the second time after one previous attack in our body they help in other t cell differentiation by enhancing the immunity suddenly. And producing a rapid resposnse to the antigen encountered .

36 ). The B cell receptor is an immunoglobin molecule. They are produced when and th2 cells with an antigen presenting cell release interlukin 4 and 5 wich causes B cell activation , the B cell takes up the antigen and a paratope structure opposite to the epitope in the antigen is produced by the B cells and they are the B cell receptors produced which now directly recognize the antigen.

37). B cells has to undergo negative selection because , some B cells may recognize self tissue as antigens and they can ellicit and autoimmune response in our body , so they undergo negative selection and B cells that recognize self tissue is eliminated by apoptosis in marrow .

38 ) B1 bcell they are found in peripheral areas like omentum and peritoneal and pleural cavities they are produced earlier mainly in the fetus , they have low affinity to antigens . They are t cell independent .

B2 b cell , they are produced in late stages of lives , they play role in acquired immunity , t cell dependent and has high affinity to antigen mostly seen in bone marrow and lymphoid tissues .