Adaptive Immunity — Cellular (T Cells & MHC)

By completing this question set, you will be able to distinguish MHC Class I from Class II molecules by their structure, expression patterns, antigen processing pathways, and the T-cell subsets they engage. You will trace T-cell activation through the three-signal model and explain why absent co-stimulation leads to anergy rather than activation. You will differentiate the five CD4+ T helper subsets (Th1, Th2, Th17, Treg, Tfh) by their differentiation signals, master transcription factors, signature cytokines, and effector functions, and predict the clinical consequences of each subset's dysfunction. You will describe how CD8+ CTLs kill target cells via perforin/granzyme and Fas/FasL pathways and explain MHC I downregulation as a viral evasion strategy. You will characterize regulatory T cells and explain how FoxP3 mutation leads to the multi-organ autoimmunity of IPEX syndrome. You will explain how superantigens bypass normal antigen processing to cause massive T-cell activation and toxic shock. Finally, you will apply the cancer immunoediting framework to explain how tumors escape immune surveillance and connect evasion mechanisms to checkpoint inhibitor therapy.