The bryostatins are macrocyclic lactones, extracted from the marine bryozoan Bugula neritina, and have been reported to be potent antineoplastic agents. Results described here demonstrate that the bryostatins may also be useful as stimulators of normal human hematopoietic cells since they can (i) directly stimulate bone marrow progenitor cells to form colonies in vitro and (ii) functionally activate neutrophils. Structure-activity studies with bryostatin congeners indicate that these stimulatory properties may be dependent on the chain length and the unsaturated nature of the acylated group at carbons 20 and 7 of the bryostatin molecule. These stimulatory properties demonstrate that the naturally occurring bryostatins can mimic many of the biological effects of multipotential granulocyte-macrophage colony-stimulating factor. Thus, the coupling of antineoplastic activity with stimulatory growth properties for normal hematopoietic cells makes this agent an excellent probe to dissect the mechanism(s) ofnormal hematopoiesis. In addition, bryostatin may represent a clinically attractive agent useful for treating bone marrow failure states.

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To assess the separate contributions of host T cells and the physical state of the antigen in the development of effective Salmonella resistance, glutaraldehyde-treated and untreated proteinand ribonucleic acid-rich extracts (E-RNA extracts) of virulent Salmonella typhimurium SR-li or attenuated S. typhimurium RIA were used to immunize Salmonella-resistant and Salmonella-susceptible strains of mice for the purpose of determining whether antigen-specific Tcell or B-cell responses were formed and, if so, which responses predominated. The resistance imparted to each mouse strain after vaccination with S. typhimurium RIA was used as the standard for comparison. The inbred mouse strains C57BL/6 and DBA/2 and their F1 hybrid (strain BDF1), outbred ICR Swiss mice, and endotoxin-resistant C3H/HeJ mice were examined for the capacity to develop resistance to lethal Salmonella infections, as well as the ability to generate antigen-reactive T cells. Only the BDF1, C3H/HeJ, and ICR Swiss mice were able to develop resistance to challenge infections mediated by the virulent SR-11 strain of S. typhimurium after vaccination with the living, attenuated RIA strain of S. typhimurium or immunization with E-RNA extracts. We developed an assay to identify the antigen-reactive rosette-forming lymphocytes present in lymph nodes and spleens of immunized mice. Levels of 0.2% or higher of theta antigenbearing, antigen-reactive rosette-forming cells were found in the lymph nodes or spleens or both of only the BDF1, C3H/HeJ, and ICR Swiss mice (i.e., in the "Salmonella responder" strains). Mouse strains C57BL/6 and DBA/2, which failed to develop resistance to lethal infections after immunization with the S. typhimurium RIA vaccine or with the E-RNA extracts, lacked effective numbers of antitheta antigen-sensitive rosette-forming cells. Modification of the effective E-RNA extracts by polymerization with glutaraldehyde resulted in a marked diminution in their abilities to induce resistance to salmonellosis in the two responder mouse strains tested (BDF1 and ICR Swiss), even though detectable levels of antibody were induced.