Conversely, if Lk >Lk0  and DLk >0 means positive, then the DNA is “positively supercoiled.”

TLS Online TPP Program

#Id: 10317

#Unit 4. Cell Communication and Cell Signaling

Cytotoxic T Cells target tumor cells

Most tumor cells, express MHC class I molecules on their surface, cytotoxic T cells can directly recognize them. 

cytotoxic T cells can result in killing of the tumor cells by two different mechanisms

TLS Online TPP Program

#Id: 10318

#Unit 4. Cell Communication and Cell Signaling

Cytotoxic T cells release granules containing the proteins perforin and granzyme-B. 

TLS Online TPP Program

#Id: 10319

#Unit 4. Cell Communication and Cell Signaling

Fas-L on the cytotoxic T cell binds to its receptor, the Fas protein on the tumor cells, an apoptotic signaling pathway in the tumor cells becomes activated, which also leads to tumor cell death. 

TLS Online TPP Program

#Id: 10320

#Unit 4. Cell Communication and Cell Signaling

The tumor cells may acquire additional oncogenic mutations that allow them to escape the immune system.

TLS Online TPP Program

#Id: 10321

#Unit 4. Cell Communication and Cell Signaling

The tumor down regulates the expression of class I MHC proteins

TLS Online TPP Program

#Id: 10322

#Unit 4. Cell Communication and Cell Signaling

Sometimes the tumor cells up-regulate the expression of anti-apoptotic proteins like BCL-2.