Signal transduction by the platelet Fc receptor

We have evaluated the mechanism by which crosslinking human platelet Fc receptor (FcR) for IgG triggers platelet aggregation and the platelet release reaction. Platelet FcR was crosslinked by incubating purified human platelets with anti-FcRII monoclonal antibody and F(ab')2 anti- mouse Ig. The resultant [Ca2+]i increase, monitored by Fura-2 and measured in the absence of extracellular Ca2+, reached a peak of 750 +/- 50 nmol/L. The effects of cyclooxygenase inhibitors, aspirin and indomethacin, and a phospholipase A2 inhibitor, dibromoacetophenone, were examined. Regardless of the inhibitor, at least 25% of the [Ca2+]i increase remained. Thrombin (0.2 U/mL) stimulated an immediate [Ca2+]i increase that reached 1.95 +/- 0.8 mumol/L. The [Ca2+]i increase generated by thrombin was only slightly reduced by these inhibitors. Crosslinking the FcRII of platelets resulted in a fivefold increase in the production of [3H]inositol phosphates, (IP) which, in the absence of extracellular Ca2+ was insensitive to aspirin. The activation of a [Ca2+]i increase along with the measured increases in IP indicate that FcRII crosslinking leads to the activation of phospholipase C (PLC). In contrast to thrombin, platelet activation via FcRII depends to a large extent on arachidonic acid metabolites. However, neither cyclooxygenase nor phospholipase A2 inhibitors completely blocked FcRII-stimulated [Ca2+]i increase. These observations led us to propose that crosslinking of platelet FcRII initially activates PLC.     

The Role of Serotonin (5-HT) in Behavioral Control: Findings from Animal Research and Clinical Implications

The neurotransmitters serotonin and dopamine both have a critical role in the underlying neurobiology of different behaviors. With focus on the interplay between dopamine and serotonin, it has been proposed that dopamine biases behavior towards habitual responding, and with serotonin offsetting this phenomenon and directing the balance toward more flexible, goal-directed responding. The present focus paper stands in close relationship to the publication by Worbe et al. (2015), which deals with the effects of acute tryptophan depletion, a neurodietary physiological method to decrease central nervous serotonin synthesis in humans for a short period of time, on the balance between hypothetical goal-directed and habitual systems. In that research, acute tryptophan depletion challenge administration and a following short-term reduction in central nervous serotonin synthesis were associated with a shift of behavioral performance towards habitual responding, providing further evidence that central nervous serotonin function modulates the balance between goal-directed and stimulus-response habitual systems of behavioral control. In the present focus paper, we discuss the findings by Worbe and colleagues in light of animal experiments as well as clinical implications and discuss potential future avenues for related research.     

Giant Mitochondria in a Cardiomyopathic Heart

Giant mitochondria (megamitochondria) measuring up to 14 µm in length and 3 µm in width are sporadically present in an exclusively interfibrillar position in the cardiomyocytes of a patient with restrictive cardiomyopathy. The number of cristae is augmented in the megamitochondria; these internal membranes are for the most part irregularly arrayed, but in certain giant mitochondria they run a parallel, zigzag course imparting a paracrystalline appearance to such organelles. Many of the giant mitochondria have one or several lucent, single membrane-bound inclusions that contain either &#102 - or &#103 -glycogen particles. Megamitochondria probably originate at least in part by fusion of adjacent organelles.     

Activated natural killer cells and interleukin-2 promote granulocytic and megakaryocytic reconstitution after syngeneic bone marrow transplantation in mice

Purified populations of natural killer (NK) cells were obtained from mice with severe combined immune deficiency (SCID). SCID spleen cells were cultured and activated with recombinant human interleukin-2 (rhIL- 2) in vitro. The activated NK cells were then transferred with syngeneic BALB/c bone marrow cells (BMC) and rhIL-2 into lethally irradiated syngeneic recipients to determine their effect on long-term hematopoietic reconstitution. On analysis, the transfer of rhIL-2- activated NK cells along with BMC resulted in significant increases in splenic and BM hematopoietic progenitor cells when compared with those for mice not receiving NK cells. Histologic and flow cytometric analysis showed a marked increase in granulocytic and megakaryocytic lineage cells present in the spleens of the mice receiving activated NK cells. Analysis of the peripheral blood indicated that the transfer of activated NK cells with BMC also significantly improved platelet and total white blood cell counts, with increases in segmented neutrophils. Erythroid recovery was not affected. Finally, lethally irradiated mice receiving activated NK cells and rhIL-2 along with limiting numbers of syngeneic BMC showed a marked increase in survival rate. These results show that the use of populations enriched for activated NK cells after syngeneic BM transplantation (BMT) has a profound enhancing effect on engraftment primarily affecting megakaryocytic and granulocytic cell reconstitution. Therefore, the transfer of activated NK cells and rhIL- 2 may be of clinical use to promote hematopoietic reconstitution after BMT.     

IgMs produced by two acquired immune deficiency syndrome lymphoma cell lines: Ig binding specificity and VH-gene putative somatic mutation analysis [published erratum appears in Blood 1994 Aug 1;84(3):995]

Two B-cell lines, 2F7 and 10C9, were established by single cell cloning from biopsies obtained from two acquired immune deficiency syndrome patients with Burkitt's lymphoma. Representation of the original tumors was verified by demonstration of (1) identical biallelic rearrangement of Ig genes for 2F7 and (2) shared idiotype for 10C9. Both cell lines displayed cell-surface Ig and secreted Ig (IgM lambda for 2F7, IgM kappa for 10C9). IgMs from both cell lines immunoprecipitated actin; in addition, 2F7 IgM lambda immunoprecipitated recombinant human immunodeficiency virus type 1 (HIV-1) gp 160. 2F7 IgM lambda did not react with other autoantigens (double-stranded and single-stranded DNA, actin, bovine serum albumin, IgG), whereas 10C9 IgM kappa reacted with human IgG. The 2F7 IgM heavy-chain variable region (VH) showed a 95% nucleotide homology with a previously sequenced VHIII germline gene, hv3019b9, whereas the 10C9 IgM VH showed a 95% homology with a previously sequenced VHIV germline gene, VH4.21. Use of minimally modified VH genes and demonstration of reactivity with chronically present antigens (ie, actin, HIV-1 gp 160, or human IgG) suggests that B cells in HIV-1-infected individuals proliferating in response to chronic antigenic stimulation may be at increased risk for lymphomagenesis.     

Comparing human and mouse salivary glands: A practice guide for salivary researchers

Mice are a widely utilized in vivo model for translational salivary gland research but must be used with caution. Specifically, mouse salivary glands are similar in many ways to human salivary glands (i.e., in terms of their anatomy, histology, and physiology) and are both readily available and relatively easy and affordable to maintain. However, there are some significant differences between the two organisms, and by extension, the salivary glands derived from them must be taken into account for translational studies. The current review details pertinent similarities and differences between human and mouse salivary glands and offers practical guidelines for using both for research purposes.     

Differential mobilization of myeloma cells and normal hematopoietic stem cells in multiple myeloma after treatment with cyclophosphamide and granulocyte-macrophage colony-stimulating factor

Peripheral blood stem cells (PBSCs) mobilized with high-dose chemotherapy and hematopoietic growth factors are now widely used to support myeloablative therapy of multiple myeloma and effect complete remissions in up to 50% of patients with apparent extension of event- free and overall survival. Because tumor cells are present not only in bone marrow, but also in virtually all PBSC harvests, it is conceivable that autografted myeloma cells contribute to relapse after autotransplants. In this study, the kinetics of mobilization of normal hematopoietic stem cells were compared with those of myeloma cells present in PBSC harvests of 12 patients after high-dose cyclophosphamide and granulocyte-macrophage colony-stimulating factor administration. CD34+ and CD34+Lin-Thy+ stem cell contents were measured by multiparameter flow cytometry, and myeloma cells were quantitated by immunostaining for the relevant Ig light chain and by a quantitative polymerase chain reaction for the myeloma-specific CDRIII sequence. Results indicated marked heterogeneity in the percentages of mobilized stem cells among different patients (0.1% to 22.2% for CD34+ cells and 0.1% to 7.5% for CD34+Lin-Thy+ cells, respectively). The highest proportions of hematopoietic progenitor cells were observed early during apheresis, with 9 of 12 patients mobilizing adequate amounts of CD34+ cells for 2 autotransplants (> 4 x 10(6)/kg) within the first 2 days, whereas peak levels (percent and absolute numbers) of myeloma cells were present on days 5 and 6 (0.5% to 22.0%). During the last days of collection, mobilized tumor cells exhibited more frequently high labeling index values (1% to 10%; median, 4.4%) and an immature phenotype (CD19+). The differential mobilization observed between normal hematopoietic stem cells and myeloma cells can be exploited to reduce tumor cell contamination in PBSC harvests.