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Functions of open MHC class I molecule conformations
Vaníčková, Marie ; Poláková, Ingrid (advisor) ; Vaníková, Šárka (referee)
The major role of MHC class I molecules in adaptive system is to present antigen peptides derived from intracellular environment on the cell surface. These peptides are recognized by CD8+ T-lymphocytes and they can also interact with NK cells via trans-interaction. MHC class I molecules are composed of a heavy chain, β2-microglobulin (β2m, light chain) and peptide, forming a closed conformation. The heavy chain is non-covalently associated with the light chain and is folded into extracellular domain (α1, α2, α3 subunits), transmembrane domain and cytoplasmic domain (with conserved motifs). Upon active metabolism, the β2m and peptide may dissociate from the MHC I heavy chain what leads to the formation of open conformations of MHC I. This conformational change causes the subunit to unfold and allow its interaction with various receptors and molecules. Open conformers of MHC I may form cis-interactions with themselves creating homodimers involved in immunological functions or they can associate with different receptors on the cell surface creating heterodimers responsible for non-immunological functions. Soluble forms of free heavy chains also exist outside of the cell surface. Cis-associations are very important as they influence signaling pathways of the cell, inhibition or activation of...
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Derivation and characterization of tumor cell lines labeled with fluorescent proteins
Majerová, Miriam ; Šmahel, Michal (advisor) ; Drbal, Karel (referee)
The effective treatment of cancer is hindered by the mechanisms of tumor cells allowing them to escape from immunosurveillance. One such mechanism is the downregulation of MHC I expression by tumor cells. As a result, CD8+ T lymphocytes are not able to eliminate tumor cells. These cells are often characterized by different expression of MHC I, which leads to the heterogeneity of the tumor environment. This thesis describes a production of a model of MHC I heterogeneity in tumors. Expression plasmids carrying genes for FP were created. Tumor cell lines TC-1, TC-1/A9 and TC-1/dB2m with different expression of MHC I molecules were successfully labeled with these plasmids. When monitoring stability of FP expression by these cell lines, a decrease was observed both in vitro and in vivo. The assumption that the cytokine environment of the tumor induces FP expression could not be confirmed because of unstable FP expression. In a tumor from a mixture of TC-1+TC-1/dB2m cell lines, it was possible to distinguish between these two lines based on the expression of β2m. In a mixture of TC- 1/A9+TC-1/dB2m lines, that could not be done due to the heterogeneity of TC-1/A9 MHC I expression. The use of combined immunotherapy showed the greatest impact on immune cell infiltration in tumors from a mixture of TC-1+...
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Antigen cross-presentation - mechanism and biological significance
Boháčová, Šárka ; Stříšovský, Kvido (advisor) ; Černý, Jan (referee)
iii Abstract Antigen cross-presentation is a process, when dendritic cells present exogenous antigens in context of MHC-I to CD8+ T lymphocytes. Unlike classical antigen presentation, this one goes crosswise, because exogenous antigens are otherwise usually presented on MHC-II and endogenous antigens on MHC-I glycoproteins. Molecular mechanism of cross-presentation has not been well established yet. Two major pathways are considered - vacuolar and cytosolic. In the vacuolar pathway, the internalised antigens are cleaved in the endosome by proteases and then loaded onto MHC-I. In the cytosolic pathway, the internalised antigens leave the endosome to be cleaved by the proteasome in the cytosol. They are then imported into the endoplasmic reticulum (ER) to by loaded onto MHC-I as in classical antigen presentation, or they go back into the endosome where the MHC-I loading machinery is trafficked. This process is mediated by ER proteins including those participating in ERAD, by Rab GTPases regulating vesicular transport, and by structures important for endosome maturation. Cross-presentation is important in medicine, because it ensures activation of CD8+ T lymphocytes against intracellular pathogens and cancer cells, and induction of tolerance at the...
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Molecules involved in immune evasion encoded within the US2-US11 genomic region of human cytomegalovirus
Kroutilová, Marie ; Němečková, Šárka (advisor) ; Lichá, Irena (referee)
Human cytomegalovirus (HCMV) from the family Herpesviridae causes lifelong latent infections in immunocompetent patients. HCMV encodes multiple molecules which interfere with host immune responses, thus helping the virus to escape from them and persist in the host. Inhibition of antigen presentation by MHC class i glycoproteins is an important immune evasion mechanism, which enables the virus to protect infected cells from recognition by CD8+ T lymphocytes. Most of the molecules inhibiting MHC class i presentation is encoded withing the US2 to US11 region of HCMV genome, including five glycoproteins (US2, US3, US6, US10 a US11) and one miRNA (US4-1). gpUS2 and gpUS3 are also able to block MHC class II antigen presentation and supress the response of CD4+ T lymphocytes. This thesis summarises current knowledge about the immune evasion molecules encoded within the US2-US11 genomic region of HCMV. Keywords: human cytomegalovirus (HCMV), immune evasion, MHC I, MHC II, US2, US3, US4-1, US6, US10, US11
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