The nude (nu/nu) mouse does not make a thymus and therefore no maturation of T c
ID: 253084 • Letter: T
Question
The nude (nu/nu) mouse does not make a thymus and therefore no maturation of T cells occurs in this animal. To elucidate which, if any, T cells are implicated in generation of autoimmune diseases, nude mice were injected with various T-cell populations as indicated below. Three months after injection, the animals were examined for the presence of various autoimmune diseases. The first number shown after each treatment is the number of animals found to have an autoimmune disease, the second number is the total number of animals that received that treatment. Treatment 1—uninjected: 0/18 Treatment 2-injected with a mixed population of T cells: 0/10 Treatment 3—injected with T cells that had been depleted of cells containing the marker CD25: 12/12 Treatment 4-injected with T cells that have been depleted of cells containing CD4 and CD25 markers: 0/10 Treatment 5 injected with T cells that have been depleted of cells containing CD8 and CD25 markers: 14/16 a. From these data, what cells are required to elicit an autoimmune disease? What cells are required to prevent an autoimmune response? Explain. b. Why were nude mice used in this study? c. Type 1 diabetes is an autoimmune disease in which the insulin-secreting islet cells in the pancreas are destroyed. To examine the role of CD4+CD25+ cells in this disease, CD4+CD25- T cells from control subjects were cultured in vitro in the absence and presence of increasing numbers of CD4+CD25+ cells from control subjects (dotted line in the figure on the next page) or diabetic patients (solid line). Proliferation (expansion) of the CD4+CD25– population is measured by uptake of radioactive thymidine, which is incorporated into replicating DNA (cpm is a measure of the radioactivity of the cells). The number of cells CD4+CD25+ cells added to the CD4+CD25- culture is presented as a ratio in which 1:0 means that no CD4+CD25+ cells are present and 1:1 means that there are equal numbers of CD4+CD25- and CD4+CD25+ cells. What do these data suggest could be a defect in patients with type 1 diabetes? Explain why such a defect might lead to diabetes.Explanation / Answer
a. CD4 + CD25- CD8- cells are required for autoimmunity because in the absence of CD4+ there is no autoimmnunity
b. Nude mice will not ellicit an immune response to foreign cells since they are immune deficient. So any immune response the mice shows is the response of the foreign immune cells they are injected with
c SInce there is a sudden decrease in proliferation of CD4 + CD25- cells in control subjects when the CD4 + CD25+ cell's ratio is increasing but there is only a gradual decrease in proliferation of CD4 + CD25- in diabetics patients, this shows that Diabetics patients have lesser number of CD4 + CD25- cells compared to patients.