I understand that Antigen Presenting Cells (APCs) like tumor cells express MHC-1 which in most cases might be altered. Before starting my main experiment, I did a preliminary experiment to determine the MHC-1 expression in tumor cells. I found almost all of them positive? Is it normal? Am I missing something? Or the antibody simply does not distinguish between altered and WT forms of MHC-1 protein?
PFA the data. Thank you all in advance.
All nucleated cells in the body express MHC-I so you should find it all all tumor and immune cells that you assess. Endogenous intracellular sources of antigen are presented by most MHC-I complexes, and APCs are special that they can also present exogenous sources of antigen (termed cross-presentation) under the right conditions. Mutations arising in tumors can skew or diminish the peptides that are ultimately presented by MHC-I complexes, masking the presentation of tumor-specific antigens that could be a target of CD8+ T cells responses. MHC-I expression can be increased by extracellular cues (IFNy), but cells that completely lack MHC-I would likely be killed by NK cells as they would appear to be a pathogen by the immune system.
Thank you, Brett for the clear explanation. greatly appreciate it.
The antibody that you are using might be directed toward an antigenic determinant shared among products of the HLA A, B and C, which would not recognize variants or mutant, so you should check the data sheet. SNU-719 cells have been reported to express low levels of MCH-I molecules, nonetheless it does not mean that the expression is absent (Int J Oncol. 2000;16:1159-1163). There are some cell lines that do not express MHC-I molecules, such as K562, but as Brett said, they are target for NK cells.
Thank you for the useful insights. Is the paper you are referring to is "The expression of MHC class I, TAP1/2, and LMP2/7 gene in human ...?" Unfortunately, I couldn't access the paper. Could you please direct me to a working link/pdf if possible. Thank you so much.
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