I have a data analysis question on my immunolgy homework. Any help to get me mov

Question

I have a data analysis question on my immunolgy homework. Any help to get me moving in the right direction would be awesome.

Here was the background information I was provided.

CD8+ T cells specific for a minor histocompatibility antigen termed H-Y can be generated by inoculating female mice with splenocytes from an H-2 matched male. An investigator interested in thymic selection set up an experiment in which recipient B6 females were thymectomized (ATx) and grafted with fetal thymi from either female or male donors. Some of the donor thymi were treated with deoxyguanosine (dGuo) before grafting, which kills macrophages and dendritic cells but not thymic epithelial cells. The details of the experimental protocol are given below.

The question I need help with is below:

1. From this experiment, what can you conclude regarding the thymic cell types responsible for negative selection of developing T cells? Explain your reasoning.

Thanks in advance!

Female donors of LN T cells used in H-Y-specific CTL assay CPM (x 10) from LN T cells mixed with 51Cr-labeled spleen cells ouse No B6 male 25.2 19.9 11.4 23.3 25.1 18.9 0.4 0.3 1.0 30.4 28.7 41.4 B6 female Normal B6 0.4 0.2 0.2 0.6 0.4 0.2 0.4 0.1 0.1 0.3 0.6 ATx B6 given female fetal thymus ATx B6 given male fetal thymus 2 ATx B6 given dGuo-treated male fetal thymus For thymus grafted mice (bottom three groups), B6 females were thymectomized, giver 1000rads, reconstituted with T cell depleted bone marrow from B6 females, then grafted with female or male fetal thymuses. Some male fetal thymi (last group) were treated in vitro with dGuo before engraftment. Following four weeks to allow full reconstitution of thymus grafted mice, all mice were inoculated with B6 male spleen cells and their LN T cells were cultured with chromium-51 loaded female or male B6 spleen cells 9 days later

Explanation / Answer

Thymus gland is a bi-lobular gland located behind the sternum and in front of heart. The thymus gland produces “T lymphocytes” (T for thymus) from the lymphoid stem cells under the influence of thymus hormones. The matured T cells (differentiated) are mainly involved in the process of cell-mediated immunity. With increasing age, the size of thymus gland decreases, which intern decrease the production of lymphocytes. This increases the risk of occurrence of infections.

T lymphocytes mainly account for about 80% of the total lymphocytes in our body. There are several types of T lymphocyte, and the major types include cytotoxic T cells, helper T cells and suppressor T cells. Cytotoxic T cells (TC) are mainly involved in cell-mediated immunity. They attack the virus infected cells or any foreign cells by direct contact with them.

From the given data,

The CD8 is a selectable marker, which is expressed by the T cells and it is involved in the selection of T cells (double positive) during negative thymic selection. This process occurs at cortico-medullary junction of thymic cortex. In this mechanism, the self-reactive T-cell will die and non-self reactive cell will survive. This process is regulated by an autoimmune regulator called AIRE.

The negative selection also requires macrophages and dendritic cells (bone marrow derived APCs), which express MHC class-I and class-II with self peptides.

Mice were made deficient in the chain of H-2M (the mouses equivalent of DM) and all their Class II expressed CLIP. In these mice, only T cells specific for CLIP, not for other self peptides, were negatively selected in the thymus and the overall number of CD4 T cells produced was reduced.

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