HDAC9 and infection: For instance, infection by Anaplasma phagocytophilum, a Gram-negative bacterium that resides in granulocytes and causes granulocytic anaplasmosis in humans, upregulates HDAC expression and the bacterial AnkA protein was shown to interact with gene regulatory regions of host chromatin silencing host cell defense genes (Garcia-Garcia et al., 2009a,b).