What does absense of MHC Class I indicate? Almost all nucleated cells will have MHC Class I molecules on their surface and their main role is to present foreign protein to cytotoxic T cells (Tc Cells) so that the cells which got infected can be cleared by these Tc cells. But in some cases, it has been observed that some tumor cells will escape killing or elimination by Tc cells by becoming MHC Class I negative, here they will not express MHC Class I molecules on their surface and thus there will not be any expression of tumor antigens to Tc cells and these will survive and will go on producing new cells and form the tumor. Like this MHC class I negative cells present within the primary tumor will develop into unnoticed micrometastases and will have an immunological equilibrium and succeeds in surviving in a dormant stage for long periods of time What does the presentation of tyrosinase indicate? The tyrosinase will cleave the tumor proteins and will express the melanoma antigens on the cell surface as peptides and overexpression of these antigens in tumor cells will result in an abnormally high density of specific peptide:MHC complexes on the cell surface making them immunogenic and provides them tolerance and is seen as tumor rejection in most of the cases. What dos decreased CTL infiltratioin indicate? It is the CD8+ cytotoxic T lymphocytes (CTLs) which will reject the tumor by infiltrating the solid tumors by recognizing the tumor antigens, and will kill those tumor cells. And to do this CTLs will try to infiltrate tumors in depth and it is done only when tumor cells express the cognate CTL antigen. If the tumor will not express the cognate antigen, CTL infiltration will not occur and the tumor cells cannot be killed and so the expression of tumor antigen on the cells will attract CTL infiltration, at the same time when the tumor antigens are not presented on these cells, it will decrease the CTL infiltration. Solution What does absense of MHC Class I indicate? Almost all nucleated cells will have MHC Class I molecules on their surface and their main role is to present foreign protein to cytotoxic T cells (Tc Cells) so that the cells which got infected can be cleared by these Tc cells. But in some cases, it has been observed that some tumor cells will escape killing or elimination by Tc cells by becoming MHC Class I negative, here they will not express MHC Class I molecules on their surface and thus there will not be any expression of tumor antigens to Tc cells and these will survive and will go on producing new cells and form the tumor. Like this MHC class I negative cells present within the primary tumor will develop into unnoticed micrometastases and will have an immunological equilibrium and succeeds in surviving in a dormant stage for long periods of time What does the presentation of tyrosinase indicate? The tyrosinase will cleave the tumor proteins and will express the melanoma antigens on the cell surface as peptides and overexpres.

1. What does absense of MHC Class I indicate?
Almost all nucleated cells will have MHC Class I molecules on their surface and their main role
is to present foreign protein to cytotoxic T cells (Tc Cells) so that the cells which got infected
can be cleared by these Tc cells. But in some cases, it has been observed that some tumor cells
will escape killing or elimination by Tc cells by becoming MHC Class I negative, here they will
not express MHC Class I molecules on their surface and thus there will not be any expression of
tumor antigens to Tc cells and these will survive and will go on producing new cells and form
the tumor. Like this MHC class I negative cells present within the primary tumor will develop
into unnoticed micrometastases and will have an immunological equilibrium and succeeds in
surviving in a dormant stage for long periods of time
What does the presentation of tyrosinase indicate?
The tyrosinase will cleave the tumor proteins and will express the melanoma antigens on the cell
surface as peptides and overexpression of these antigens in tumor cells will result in an
abnormally high density of specific peptide:MHC complexes on the cell surface making them
immunogenic and provides them tolerance and is seen as tumor rejection in most of the cases.
What dos decreased CTL infiltratioin indicate?
It is the CD8+ cytotoxic T lymphocytes (CTLs) which will reject the tumor by infiltrating the
solid tumors by recognizing the tumor antigens, and will kill those tumor cells. And to do this
CTLs will try to infiltrate tumors in depth and it is done only when tumor cells express the
cognate CTL antigen. If the tumor will not express the cognate antigen, CTL infiltration will not
occur and the tumor cells cannot be killed and so the expression of tumor antigen on the cells
will attract CTL infiltration, at the same time when the tumor antigens are not presented on these
cells, it will decrease the CTL infiltration.
Solution
What does absense of MHC Class I indicate?
Almost all nucleated cells will have MHC Class I molecules on their surface and their main role
is to present foreign protein to cytotoxic T cells (Tc Cells) so that the cells which got infected
can be cleared by these Tc cells. But in some cases, it has been observed that some tumor cells
will escape killing or elimination by Tc cells by becoming MHC Class I negative, here they will
not express MHC Class I molecules on their surface and thus there will not be any expression of
tumor antigens to Tc cells and these will survive and will go on producing new cells and form
the tumor. Like this MHC class I negative cells present within the primary tumor will develop
into unnoticed micrometastases and will have an immunological equilibrium and succeeds in

2. surviving in a dormant stage for long periods of time
What does the presentation of tyrosinase indicate?
The tyrosinase will cleave the tumor proteins and will express the melanoma antigens on the cell
surface as peptides and overexpression of these antigens in tumor cells will result in an
abnormally high density of specific peptide:MHC complexes on the cell surface making them
immunogenic and provides them tolerance and is seen as tumor rejection in most of the cases.
What dos decreased CTL infiltratioin indicate?
It is the CD8+ cytotoxic T lymphocytes (CTLs) which will reject the tumor by infiltrating the
solid tumors by recognizing the tumor antigens, and will kill those tumor cells. And to do this
CTLs will try to infiltrate tumors in depth and it is done only when tumor cells express the
cognate CTL antigen. If the tumor will not express the cognate antigen, CTL infiltration will not
occur and the tumor cells cannot be killed and so the expression of tumor antigen on the cells
will attract CTL infiltration, at the same time when the tumor antigens are not presented on these
cells, it will decrease the CTL infiltration.