This disclosure provides, in certain embodiments, methods for generating and using extracts of Pyrularia (e.g., Pyrularia pubera) and/or an 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. Other embodiments of the invention provide methods of producing extracts of the invention, as well as purified bioactive components thereof, including particularly bacterial LPS.Cette invention concerne, dans certains modes de réalisation, des procédés de génération et dutilisation dextraits de Pyrularia (par exemple de pyrularia pubera) et/ou dune bactérie épiphyte/endophyte associée à celle-ci, soit seule ou en combinaison avec un ou plusieurs immunostimulants classiques ou des agents anti-inflammatoires, pour la modulation du système immunitaire dun sujet. Linvention concerne également des compositions qui comprennent des extraits de Pyrularia spécifiques, des bactéries isolées à partir de tissu de Pyrularia (en particulier lespèce Pantoea) et des extraits provenant de telles bactéries. La présente invention concerne également des composants purifiés dextraits de Pyrularia et/ou dextraits de bactéries épiphytes/endophytes, lesquels extraits présentent des activités mitogènes ou cytotoxiques. Les compositions
