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PubMed1980

Development of antibody formation in germ-free and conventionally reared rabbits: the role of intestinal lymphoid tissue in antibody formation to E. coli antigens.

The occurrence of cells which produce 'natural" bactericidal and haemolytic antibodies (the so-called background plaques) was studied by the plaque method in lymphatic tissues of germ-free and conventionally reared rabbits of various ages. In conventional rabbits the cells which produce "natural" bactericidal antibodies against E. coli 086 appear early after birth in organized intestinal lymphatic tissue, their number increases during development, then they appear in mesenteric lymph nodes and spleen and their number decreases due to aging. Natural haemolytic antibodies are produced throughout the life predominantly in the spleen of conventional rabbits. In germ-free rabbits the appearance of "natural" bactericidal or haemolytic antibodies was not demonstrated during the tested period of 16 weeks of life. Also when comparing the immunological capacity after parenteral immunization or after stimulation of cells from various organs cultivated in diffusion chambers, the response in germ-free rabbits was very low or lacking. The differences between the reactivity of germ-free and conventional rabbits were especially marked when studying the specific and non-specific (polyclonal) response after administration of E. coli suspension. The nature and possible causes underlying the differences in immunological reactivity in various species of germ-free animals are discussed.

Animals↗
PubMed2006

Sequential formation of yellow, red, and orange 1-phenyl-3,3-biphenylene-allene dimers prior to blue tetracene formation: Helicity reversal in trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane.

1-Phenyl-3,3-biphenyleneallene (2), the base-catalyzed rearrangement product of 9-phenylethynylfluorene (1) yields a yellow, head-to-tail dimer 6 that, upon gentle warming, is converted to the red tail-to-tail isomer trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (7), in which the two fluorenylidene moieties severely overlap. The helical sense of the fluorenylidene moieties in 7 matches that of the phenyl substituents, and the interplanar angle between the fluorenylidene moieties is 41 degrees . At 80 degrees C, 6 isomerizes to orange cis-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (8), which at 110 degrees C is converted to orange trans diastereomer 9, whereby the helicity of the overlapping fluorenylidene moieties is reversed from that in 7 such that they are aligned with the ring hydrogen atoms, and the interplanar angle between the fluorenylidene moieties is now 60 degrees . At 180 degrees C, 6 rearranges to dispirodihydrotetracene 3 and blue, electroluminescent diindenotetracene 4, which is readily oxidized to peroxide 5. In the solid state, both 3 and 4 adopt structures with Ci symmetry (only an inversion center) such that the central polycyclic framework is nonplanar. Deprotonation of yellow head-to-tail allene dimer 6 with tBuOK in DMSO and reprotonation with HOAc yields the [1,3]-hydrogen migration product 10, in which the proton originally on the cyclobutane ring is now sited at C9 on the exocyclic fluorenyl substituent. Analogously, deprotonation and reprotonation of orange dimer 9 furnishes [1,3]-hydrogen migration product 11. Side product 17, formed during the synthesis of 1 from 9-phenylethynylfluoren-9-ol, BF3 and Et3SiH, was shown to be a silyl-indene spiro-linked to C9 of fluorene. All products were characterized by NMR spectroscopy and X-ray crystallography, and the mechanisms of these interconversions are discussed.

Journal Article↗