Abstract: This disclosure provides, in certain embodiments, methods for generating and using extracts of Pyrularia (e.g., Pyrularia pubera) and/or epiphytic/endophytic bacteria associated therewith, either alone or in combination with conventional immunostimulant(s) or anti-inflammatory agents, for modulation of the immune system of a subject. Also provided are compositions that include specific Pyrularia extracts, bacteria isolated from Pyrularia tissue (in particular, Pantoea species), and extracts of from such bacteria. Also provided herein are purified components of Pyrularia extracts and/or extracts from the epiphytic/endophytic bacteria, which extracts exhibit mitogenic or cytotoxic activities. Compositions provided herein can be used for the treatment of neutropenia subsequent to chemotherapy, and for the treatment of immune deficiency (e.g., such as is caused by toxic chemotherapy, disease, or advancing age), as well as in other immune-stimulatory methods.