Von der Stammzelle zum Lymphozyten

Zusammenfassung: Zwei Typen von pluripotenten Stammzellen sind die Ursprünge der Zellen des angeborenen und des adaptiven Immunsystems wie auch von essenziellen Elementen kooperierender Umgebungen dieses Systems. Pluripotente hämatopoietische Stammzellen und die ihnen untergeordneten, subspezialisierten Progenitorzellen bilden - ein Leben lang - die roten Blutkörperchen, Blutplättchen, myeloiden und lymphoiden Zellen dieses kontinuierlich sich erneuernden Zellsystems. Pluripotente mesenchymale Stammzellen generieren, neben anderen Typen von differenzierten Zellen, Chondrozyten, epitheliale Zellen, Adipozyten und Osteoblasten. Dieses Osteoblasten produzieren nicht nur Knochen, die primären Orte für die hämatopoietische Zellentwicklung, sondern sie interagieren auch direkt mit den hämatopoietischen Stammzellen und Progenitorzellen - wie auch mit dem reifen, antigenerfahrenen "Gedächtnis"-Typ von Lymphozyten, die nach erfolgreichen Kämpfen mit Antigenen an die Stelle ihres Ursprungs zurückkehren. Diese Interaktionen geschehen durch Zell-Zell-Kontakte wie auch durch Zytokin-Zytokinrezeptor-Erkennungen in sogenannten "Nischen" und induzieren und leiten die Entwicklungen der hämatopoietischen Zellen. Diese frühen Phasen der hämatopoietischen Entwicklung sind antigenunabhängig, weil die Zellen des adaptiven Immunsystems, die Lymphozyten, noch keine antigenspezifischen Rezeptoren entwickelt haben. Sobald diese Zellen aber T-Zell- und B-Zell-Rezeptoren für Antigen exprimieren, werden sie dem Druck von negativer und positiver Selektion ausgesetzt, erst von Autoantigenen in den primären lymphoiden Organen, dann, nach Reifung und Wanderung in die sekundären lymphoiden Organe, auch von externen, fremden Antigenen. Die Repertoire dieser Lymphozyten, die TcR und BcR exprimieren, adaptieren also an die Umgebung von Antigenen des eigenen Körpers, und an die der externen, fremden Einflüsse. Während Zell-Zell-Kontakte mit kooperierenden nichthämatopoietischen wie auch hämatopoietischen Zellen, und Zytokin-Zytokinrezeptor-Interaktionen weiterhin die zellulären Reaktionen induzieren, die zu Proliferation, Differenzierung und/oder programmiertem Zelltod (Apoptose) der reifen hämatopoietischen Zellen führen können, sind diese Reaktionen jetzt aber durch die spezifischen Kontakte von Antigen mit den antigenspezifischen Rezeptoren, TcR's und BcR's, dominier

Plankton diatoms of the "Toko-Maru" voyage (Brazil coast)

Estuda-se, no presente trabalho, o material coletado ao longo da costa brasileira pelo navio "Toko-Maru". As coletas podem ser distribuídas em dois grupos tais como: quatro amostras provenientes do sul e as restantes 14 da circumvizinhança da desembocadura do Rio Amazonas, abaixo e acima do Equador. Esses dois grupos são bem distintos. As quatro amostras do sul apresentam muita semelhança com o material das províncias riograndense e uruguaia. Nelas prevalecem formas discoides de Actinocyclus e Coscinodiscus. O autor encontrou Chaetoceros Okamurai Ikari, nova para a América do Sul, o mesmo acontecendo com Nitzschia pungens var. atlântica Cie re. Em relação a Rhizosolenia hyalina Ostenfeld, acredita o autor ser esta a primeira vez em que essa diatomácea do sul da Asia é referida para o Atlântico. Descreve o autor uma espécie nova: Actinocyclus brasiliensis e uma nova variedade : Rhizosolenia setigera Brightwell var. daga. O exame das amostras permitiu concluir que o material das vizinhanças do Amazonas é pobre em formas, consistindo principalmente de Coscinodiscus concinnus W. Smith e, em menor quantidade, de C. oculus iridis Ehrenberg. Essas duas diatomáceas acham-se acompanhadas por Nitzschia pungens vdr. atlántica Cleve, não raro confundida com N. delicatissima Cleve

Frequencies of mitogen-reactive B cells in the mouse. I. Distribution in different lymphoid organs from different inbred strains of mice at different ages

Frequencies of mitogen-reactive B cells have been determined in vitro under culture conditions which allow every growth-inducible B cell to grow and mature into a clone of Ig-secreting PFC. The frequencies of LPS-reactive B cells in the spleen of 6- to 8-wk old mice were between 1 in 3 and 1 in 10 splenic B cells from the following inbred strains of mice: C3H/Tif; BALB/c; BALB/c ν/ν; C57BL/6J; DBA/2J; C57BL/6J x DBA/(2J)F(1); and CBA and A/J. Very similar frequencies are found for lipoprotein-reactive B cells in BALB/c, BALB/c ν/ν, C3H/Tif, and C3H/HeJ mice. No LPS-reactive cells but normal frequencies of lipoprotein-reactive cells were found in C3H/HeJ mice, genetically nonreactive to LPS. SJL mice had significantly lower frequencies of LPS- and of lipoprotein-reactive B cells (1 in approximately 30 B cells). The number of LPS- and of lipoprotein-reactive B cells in spleen was dependent upon the age of the mouse. Newborn spleen contained approximately 10 percent of the number of reactive cells found at 6- to 8-wk of age. From there the frequencies declined again to drop below 5 percent of the maximal number at ages beyond 11 mo. LPS-reactive B cells yielding IgM- and IgG-PFC responses could be found in mesenteric lymph nodes, bone marrow, thymus, thoracic duct, and peripheral blood of 6- to 8-wk old mice. Their frequencies were one in three to five lymph node cells, 1 in 50 to 100 bone marrow cells, one in 10(5) thymus cells, and 1 in 20 to 40 thoracic duct or peripheral blood cells

Frequencies of mitogen-reactive B cells in the mouse. II. Frequencies of B cells producing antibodies which lyse sheep or horse erythrocytes, and trinitrophenylated or nitrodophenylated sheep erythrocytes

The B-cell mitogens LPS and lipoprotein stimulate 20-35 percent of all B cells in the spleen of 6- to 8-wk old C3H/Tif mice, as determined by limiting dilution analysis of precursors. Each reactive cell grows to a clone of IgM-secreting PFC, enumerated in a hemolytic plaque assay detecting all IgM secreting cells, regardless of v-region specificity. We have used these mitogens to reveal the total repertoire of Ig specificities produced by these mitogen-reactive B cells. We have determined in plaque assays with six different target erythrocytes the number of spleen cells limiting to one the number of mitogen-reactive B cells detected as specific IgM-secreting clones in each of these plaque assays. By this method, the absolute frequencies of precursor B cells with defined v-gene specificities could be calculated, for at least, one third of all B cells. The frequencies of specific IgM-plaque-forming B-cell clones within the total pool of mitogen-reactive B cells was 1 in 10 for NIP(12),-SRC, 1 in 50 for TNP(12)- SRC, 1 in 100 for NIP(1)-SRC, 1 in 160 for TNP(3)- SRC, 1 in 500 for HRC, and 1 in 1,000 for SRC. These frequencies were the same in the LPS- and in the lipoprotein-reactive B-cell population for TNP(30)- SRC and SRC

IgM-producing tumors in the BALB/c mouse: a model for B-cell maturation

Five adjuvant induced BALB/c tumors producing IgM—McPc 1748, W 3469, TEPC 183, McPc 774, and Y 5781—were characterized morphologically by electron microscopy, analysis of the distribution of surface-bound and intracytoplasmic IgM using immunofluorescence, and by biochemical study of IgM synthesis, turnover, and secretion. The cells of different tumors appear to represent different stages in B-cell maturation when compared to normal, lipopolysaccharide-stimulated B cells. Thus, McPc 1748 tumor cells resemble 10–25-h stimulated normal B cells, 3469 cells resemble 20–35-h stimulated B cells, TEPC 183 cells resemble 45–65-h stimulated B cells, Y 5781 cells resemble 80–110-h stimulated B cells, and McPc 774 cells resemble 100–130-h stimulated B cells