How host cell behavior alters by pathogen?

Answer 1

A cell transmutes a stimulus on the outside of the plasma membrane into changes in the cell's physiological program by means of intracellular signaling pathways. These are usually triggered by the ligation of an external ligand, such as a cytokine or a Leishmania surface molecule, to a receptor on the cell surface. This ligation causes activation of the receptor, commonly by phosphorylation and/or conformational changes, resulting in activation of second messengers within the cytosol. These second messengers are often protein kinases, which then phosphorylate other kinases to continue a cascade that ultimately results in the activation of effector molecules, such as transcription factors or actin filaments, and causing a change in the cell's behavior. It should be emphasized that the activity of an intracellular pathway is normally determined by a balance of both positive and negative regulation. Activation of a given kinase cascade will often result in the activation of its opposing phosphatases, in a classic example of negative feedback. Many prokaryotic and eukaryotic pathogens, including Leishmania, have evolved various strategies to exploit host cell signaling regulatory mechanisms by distorting this balance between positive and negative influences.