SummaryIn this report we have investigated macrophage (M~b) activity and tumor necrosis factor (TNF-ot) production during graft-vs.-host disease (GVHD). TNF-ot production by M~b requires two signals: priming of M~b by interferon followed by triggering of TNF-c~ production and release by lipopolysaccharide (LPS). The state of M~ activation was examined in nonirradiated B6AF1 recipient mice injected with either 60 x 106 (acute GVHD) or 30 x 106 (nonlethal GVHD) parental B6 lymphoid cells. During the early phase of acute GVHD, administration of normally sublethal amounts of LPS-triggered release of significant amounts of TNF-ot into the serum resulting in death of the animals within 36 h. Normal animals treated with the same dose of LPS neither died nor produced detectable amounts of serum TNF-ot. In vitro studies demonstrated that M~ were primed during GVHD. The level of Mq~ priming was greater during acute GVHD than nonlethal GVHD since 100-fold less LPS was required to trigger killing of a TNF-ot-sensitive cell line by M~b from acute GVHD animals. The amount of TNF-ot released into the serum after LPS injection increased during the course of the GVHD and was significantly greater in acute GVH-reactive mice. Endogenous LPS was detected in the serum of acute GVHreactive animals coincident with the onset of mortality. The data provide evidence that during GVHD M~b are primed as a result of the allogeneic reaction and that endogenous LPS therefore triggers Mq~ production of TNF-c~ resulting in the symptoms characteristic of acute GVHD.

NIH 3T3 cells cotransfected with the human c-fms proto-oncogene together with a 1.6-kilobase cDNA clone encoding a 256-amino-acid precursor of the human mononuclear phagocyte colony-stimulating factor CSF-1 (M-CSF) undergo transformation by an autocrine mechanism. The number of CSF-1 receptors on the surface of transformed cells was regulated by ligand-induced receptor degradation and was inversely proportional to the quantity of CSF-1 produced. A tyrosine-to-phenylalanine mutation at position %9 near the receptor carboxyl terminus potentiated its transforming efficiency in cells cotransfected by the CSF-1 gene but did not affect receptor downmodulation. CSF-1 was synthesized as an integral transmembrane glycoprotein that was rapidly dimerized through disulfide bonds. The homodimer was externalized at the cell surface, where it underwent proteolysis to yield the soluble growth factor. Trypsin treatment of viable cells cleaved the plasma membrane form of CSF-1 to molecules of a size indistinguishable from that of the extracellular growth factor, suggesting that trypsinlike proteases regulate the rate of CSF-1 release from transformed cells. The data raise the possibility that this form of membrane-bound CSF-1 might stimulate receptors on adjacent cells through direct cell-cell interactions.

Mast cells are critical components of innate and adaptive immunity that differentiate in tissues in situ from circulating committed progenitor cells. We now demonstrate that human cord blood-derived mast cell progenitors are susceptible to infection with macrophagetropic (M-tropic) and dualtropic human immunodeficiency virus type 1 (HIV-1) isolates but not with T-cell-tropic (T-tropic) strains. Mast cell progenitors (c-kit؉ cells with chloroacetate esterase activity) were purified from 4-week-old cultures of cord blood mononuclear cells maintained in stem cell factor, interleukin-6 (IL-6), and IL-10 using a CD14 depletion column. These progenitors expressed CCR3, CCR5, and CXCR4, as well as low levels of CD4. When infected in vitro with viruses pseudotyped with different HIV and simian immunodeficiency virus envelope glycoproteins, only M-tropic and dualtropic, but not T-tropic, viruses were able to enter mast cell progenitors. Both the CCR5-specific monoclonal antibody 2D7 and TAK-779, a nonpeptide inhibitor of CCR5-mediated viral entry, blocked HIV-1 strain ADA infection by >80%. Cultures infected with replication-competent virus produced progressively increasing amounts of virus for 21 days as indicated by p24 antigen detection. Mast cell progenitors that were exposed to an M-tropic, green fluorescent protein-expressing HIV-1 strain exhibited fluorescence indicative of viral entry and replication on a single-cell level and retained virus production during differentiation. The trafficking of mast cell progenitors to multiple tissues, combined with the long life span of mature mast cells, suggests that they could provide a widespread and persistent HIV reservoir in AIDS.

Anti-IgE therapy with omalizumab, a recombinant humanized monoclonal antibody, has anti-inflammatory effects in allergic asthma and rhinitis. Although omalizumab has been exceptionally safe, reactions after its administration have been reported. The goal of this study was to assess two patients who experienced apparent anaphylaxis after omalizumab administration. Two cases of apparent anaphylaxis after omalizumab administration are reported with diagnostic evaluation using skin testing and unique IgE and IgG anti-omalizumab serological assays. At the time of evaluation, both atopic asthmatic patients had total (free and bound) serum IgE levels of 199 kIU/L (100% free) and 200 kIU/L (80% free and 20% bound), respectively. Epicutaneous skin tests to omalizumab were negative at 150 mg/mL of omalizumab in both subjects and the nonexposed negative control subject. Intradermal skin tests were positive at 0.15 mg/mL in subject 1 and negative at 1.5 mg/mL of omalizumab in subject 2 and the control subject. Intradermal testing to polysorbate produced significant wheal/flare reaction in subject 2 but not in the negative control subject. Serological assays for IgE or IgG antibodies reactive with omalizumab were negative. The in vitro and in vivo immunologic data support the conclusion that the adverse reactions experienced by two patients after omalizumab administration after more than a year of successful omalizumab therapy for asthma were likely anaphylactoid in nature. Polysorbate, an excipient in omalizumab, is known to cause similar reactivity to other medicines and is the most likely cause of these reactions.

No abstract