Immunocytochemical localization of fibrinogen on washed human platelets. Lack of requirement for fibrinogen during adenosine diphosphate-induced responses and enhanced fibrinogen binding in a medium with low calcium levels

The association of fibrinogen with washed human platelets was examined by immunocytochemistry during aggregation induced by adenosine diphosphate (ADP) and during deaggregation. The platelets were suspended either in a medium containing 2 mmol/L Ca2+ or in a medium containing no added Ca2+ (20 mumol/L Ca2+). Platelets were fixed at several times during aggregation and deaggregation, embedded in Lowicryl K4M, sectioned, incubated with goat antihuman fibrinogen, washed, reacted with gold-labeled antigoat IgG, and prepared for electron microscopy. To determine whether the method detected fibrinogen associated with the platelets, the platelets were pretreated with chymotrypsin (10 U/mL) and aggregated by fibrinogen; gold particles were apparent not only in the alpha granules but on the platelet surface and between adherent platelets as well. In the medium with 2 mmol/L Ca2+, ADP caused extensive aggregation of normal platelets in the presence of fibrinogen (0.4 mg/mL), and gold particles were evident between the adherent platelets and on the platelet surface; when the platelets deaggregated, gold was no longer present on the surface. In a medium without added Ca2+, ADP caused extensive aggregation in the presence of fibrinogen, and large numbers of gold particles were on the platelet surface and even more between adherent platelets. In this medium, the platelets did not deaggregate, and by five minutes, the granules appeared to be swollen or fused. In the absence of external fibrinogen, ADP caused the formation of small aggregates, and fibrinogen was not detected between adherent platelets. Thus, the association of fibrinogen with the platelet surface enhances platelet aggregation but is not essential for the ADP-induced formation of small aggregates. The association of fibrinogen with platelets is greater under conditions in which platelets release their granule contents and do not deaggregate because both endogenous and exogenous fibrinogen take part in aggregation.     

Role of the Plasmodium falciparum mature-parasite-infected erythrocyte surface antigen (MESA/PfEMP-2) in malarial infection of erythrocytes

During intraerythrocytic growth of Plasmodium falciparum, several parasite proteins are transported from the parasite to the erythrocyte membrane, where they bind to membrane skeletal proteins. Mature- parasite-infected erythrocyte surface antigen (MESA) has previously been shown to associate with host erythrocyte membrane skeletal protein 4.1. Using a spontaneous mutant of P falciparum that has lost the ability to synthesize MESA and 4.1-deficient erythrocytes, we examined growth of MESA(+) and MESA(-) parasites in normal and 4.1-deficient erythrocytes. Viability of MESA(+) parasites was reduced in 4.1- deficient erythrocytes as compared with that for normal erythrocytes, but MESA(-) parasites grew equally well in 4.1-deficient and normal erythrocytes. Cytoadherence of MESA(+)- and MESA (-)-parasitized normal and 4.1-deficient erythrocytes to C32 melanoma cells was similar, indicating that neither protein 4.1 nor MESA plays a major role in cytoadherence of infected erythrocytes. Localization of MESA in normal and 4.1-deficient erythrocytes was examined by confocal microscopy. MESA was diffusely distributed in the cytosol of 4.1-deficient erythrocytes but was membrane-associated in normal erythrocytes. These findings suggest that MESA binding to protein 4.1 plays a major role in intraerythrocytic parasite viability.     

The sickle gene polymorphism in North Africa

Analysis of the restriction endonuclease Hpa 1-beta globin gene linkage has been performed in a predominantly Arab population of North Africa possessing the sickle (beta A) gene is found associated with a 7.6 kilobase) or 7.0 kb Hpa 1 fragment (54/54 assignable beta A genes), whereas the beta S gene is found associated with a 13 kb Hpa 1 fragment (42/42 assignable beta S genes). The results demonstrate a very tight linkage of the beta S gene to the 13 kb Hpa 1 fragment as well as a very low probability that a beta A gene will be found on a 13 kb Hpa 1 fragment. Thus, the North African population presents a nearly ideal opportunity for prenatal diagnosis solely by Hpa 1-beta globin gene linkage analysis. Additionally, the evidence supports the hypothesis that the beta S gene flowed from West Africa rather than from Arab populations in the Middle East.     

Increased expression of platelet IgG Fc receptors in immune heparin- induced thrombocytopenia

Our previous finding that heparin-dependent antibodies in heparin- induced thrombocytopenia (HIT) bind to platelets via platelet IgG Fc receptors (FcRs) prompted this study. Platelet FcRs in 16 patients with HIT, 23 control patients, and 42 normal subjects were studied. Patients with HIT had substantially increased platelet FcRs during the acute illness. Those who suffered serious thrombotic complications or died shortly after diagnosis had significantly more FcRs per platelet than those with milder disease. Consistent with their increased FcRs, platelets of patients with HIT showed increased aggregation reactivity to aggregated IgG and heparin-dependent antibodies. Platelet FcRs in patients with HIT remained elevated for 1 to 3 months after the acute illness then stabilized to a mean value not significantly different from either control group. The increased expression of FcRs on HIT platelets and their increased reactivity to heparin-dependent antibodies may contribute to the pathogenesis of thrombocytopenia and thrombosis in HIT.     

Long-term outcome of aplastic anemia in adults treated with antithymocyte globulin: comparison with bone marrow transplantation

The outcome of 155 adult aplastic anemia (AA) patients treated with antithymocyte globulin (ATG, Upjohn, Kalamazoo, MI) at University of California, Los Angeles from 1977 to 1988 was evaluated. The median survival of the 146 patients who did not undergo bone marrow transplantation was 5.6 years, with 49% +/- 4% surviving more than 6 years. The most important predictor of survival was positive response to ATG (P < 0.001), which was observed in 48% of patients. Among pretreatment variables, disease severity was the best predictor of survival. Patients with moderate AA (MAA) had significantly better survival than those with severe (SAA) or very severe (VSAA) disease (P = 0.04). The 6-year actuarial survival rates of the three groups were 71% +/- 9%, 48% +/- 7% and 38% +/- 7%, respectively. Cox regression analysis found disease severity to be the only pretreatment variable significantly associated with survival (P = .02). Patient age, sex, disease etiology, concurrent treatment with androgens, or duration of ATG therapy were not associated with differences in survival or response to ATG. Late clonal hematologic complications (ie, myelodysplasia, acute myelogenous leukemia) were observed in 5 of the 77 patients followed for more than 2 years after ATG treatment. In addition, one case of non-Hodgkin's lymphoma and three solid tumors occurred in the ATG-treated patients. The survival of 56 ATG-treated patients with SAA or VSAA between the ages of 16 and 43 did not differ significantly from that of 55 adult AA patients who underwent bone marrow transplant (BMT) during the same time period (P = 0.6). However, 6-year survival rates improved from 43% for patients transplanted before 1984, to 72% for those who underwent BMT between 1984 and 1989. In contrast, there was no difference in the survival rates of patients treated with ATG during these two time periods (46% v 45%, respectively). The results suggest a superior long-term outcome for adult patients with SAA treated with BMT rather than with ATG alone, using current protocols.     

Delayed infusion of immunocompetent donor cells after bone marrow transplantation breaks graft-host tolerance allows for persistent antileukemic reactivity without severe graft-versus-host disease

The development of graft-host tolerance after bone marrow transplantation (BMT) is crucial to avoid the problems of graft-versus- host disease (GVHD) and graft rejection. GVHD can be eliminated by depleting mature donor T cells from the BM inoculum, thereby facilitating the development of graft-host tolerance. However, T-cell depletion often results in an increased incidence of graft rejection and an increased frequency of leukemia relapse. Thus, although graft- host tolerance is a desirable outcome, it can pose a significant threat to leukemia-bearing hosts. Using a major histocompatability complex (MHC)-matched allogeneic model of BMT (B10.BR into AKR), we found that irradiated recipients given donor BM alone displayed mixed T-cell chimerism and did not develop GVHD. Graft-host tolerance developed by 8 weeks after BMT in these chimeras, and they were susceptible to low- dose leukemia challenge. When sufficient numbers of donor spleen cells, as a source of T-cells, were added to the BM graft, AKR hosts developed severe and lethal GVHD. Antihost reactive donor T cells persisted in chimeras undergoing GVHD, indicating that graft-host tolerance did not develop. When administration of the spleen cells was delayed for 7 to 21 days after BMT, there was significantly less mortality because of GVHD. Day 21 was the optimal time for infusion of cells without development of GVHD. Graft-host tolerance was broken by the delayed infusion of donor cells, as indicated by the persistence of antihost- reactive donor T cells in these chimeras in T-cell receptor cross- linking and mixed lymphocyte reaction assays. Importantly, the persistence of antihost-reactive donor T cells correlated with along- term antileukemic effect that was still present at 100 days after transplant. Multiple infusions of immunocompetent donor cells could be administered without increasing the risk for GVHD if delayed until 21 days post-BMT. Delayed infusions of donor spleen cells also resulted in a long-term antileukemic effect in the absence of GVHD in an MHC- haplotype-mismatched model of BMT (SJL into [SJL x AKR]F1). Although delayed infusion of normal donor cells did not induce GVHD, spleen cells from donors previously sensitized to host alloantigens induced GVHD when infused 21 days after BMT. Thus, the ability of previously activated cells to induce GVHD was not inhibited in the same manner as naive cells. Results from limiting dilution analysis assays indicated that alloactivated interleukin-2-secreting CD4+ T cells were preferentially inhibited over cytolytic T cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Timed sequential chemotherapy of cytoxan-refractory multiple myeloma with cytoxan and adriamycin based on induced tumor proliferation

Malignant plasma cell proliferation and induced humoral stimulatory activity (HSA) occur in vivo at a predictable time following drug administration. Sequential sera from 11 patients with poor-risk multiple myeloma (MM) undergoing treatment with Cytoxan (CY) 2400 mq/sq m were assayed for their in vitro effects on malignant bone marrow plasma cell tritiated thymidine (3HTdR) incorporation. Peak HSA was detected day 9 following CY. Sequential changes in marrow malignant plasma cell 3HTdR-labeling indices (LI) paralleled changes in serum activity, with peak LI occurring at the time of peak HS. An in vitro model of chemotherapy demonstrated that malignant plasma cell proliferation was enhanced by HSA, as determined by 3HTdR incorporation assay, 3HTdR LI, and tumor cells counts, and that stimulated plasma cells were more sensitive to cytotoxic effects of adriamycin (ADR) than were cells cultured in autologous pretreatment serum. Based on these studies, we designed a clinical trial to treat 12 CY-refractory poor- risk patients with MM in which ADR (60 mg/sq m) was administered at the time of peak HSA and residual tumor cell LI (day 9) following initial CY, 2400 mg/m (CY1ADR9). Eight of 12 (67%) responded to timed sequential chemotherapy with a greater than 50% decrement in monoclonal protein marker and a median survival projected to be greater than 8 mo duration (range 4-21+ mo). These clinical results using timed sequential CY1ADR9 compare favorably with results obtained using ADR in nonsequential chemotherapeutic regimens.     

Morphometric analysis of temporomandibular joint elements

Purpose

To study the morphology of temporomandibular joint (TMJ) elements and examine the feasibility of a novel biofidelic articular disc casting technique.

Activation of southern white rhinoceros (Ceratotherium simum simum) estrogen receptors by phytoestrogens: potential role in the reproductive failure of captive-born females?

The captive southern white rhinoceros (SWR; Ceratotherium simum simum) population serves as an important genetic reservoir critical to the conservation of this vulnerable species. Unfortunately, captive populations are declining due to the poor reproductive success of captive-born females. Captive female SWR exhibit reproductive problems suggested to result from continual ovarian follicular activity and prolonged exposure to endogenous estrogen. However, we investigated the potential role of exogenous dietary phytoestrogens in the reproductive failure of SWR by cloning and characterizing in vitro phytoestrogen binding and activation of recombinant SWR estrogen receptors (ESR). We compared those characteristics with recombinant greater one-horned rhinoceros (GOHR; Rhinoceros unicornis) ESR, a species that receives similar captive diets yet reproduces relatively well. Our results indicate that phytoestrogens bind rhino ESR in a manner similar to other vertebrate species, but there are no differences found in phytoestrogen binding affinity of SWR ESR compared with GOHR ESR. However, species-specific differences in ESR activation by phytoestrogens were detected. The phytoestrogen coumestrol stimulated greater maximal activation of SWR ESR1 than GOHR ESR1. SWR ESR2 were also more sensitive to phytoestrogens and were activated to a greater extent by both coumestrol and daidzein. The concentrations in which significant differences in ESR activation occurred (10(-7) to 10(-5) m) are consistent with circulating concentrations measured in other vertebrate species. Taken together, these findings suggest that phytoestrogens potentially pose a risk to the reproductive health of captive SWR. However, additional studies are needed to further clarify the physiological role of dietary phytoestrogens in the reduced fertility of this species.     

Alkyltransferase-like protein (Atl1) distinguishes alkylated guanines for DNA repair using cation–π interactions

Alkyltransferase-like (ATL) proteins in Schizosaccharomyces pombe (Atl1) and Thermus thermophilus (TTHA1564) protect against the adverse effects of DNA alkylation damage by flagging O⁶-alkylguanine lesions for nucleotide excision repair (NER). We show that both ATL proteins bind with high affinity to oligodeoxyribonucleotides containing O⁶-alkylguanines differing in size, polarity, and charge of the alkyl group. However, Atl1 shows a greater ability than TTHA1564 to distinguish between O⁶-alkylguanine and guanine and in an unprecedented mechanism uses Arg69 to probe the electrostatic potential surface of O⁶-alkylguanine, as determined using molecular mechanics calculations. An unexpected consequence of this feature is the recognition of 2,6-diaminopurine and 2-aminopurine, as confirmed in crystal structures of respective Atl1-DNA complexes. O⁶-Alkylguanine and guanine discrimination is diminished for Atl1 R69A and R69F mutants, and S. pombe R69A and R69F mutants are more sensitive toward alkylating agent toxicity, revealing the key role of Arg69 in identifying O⁶-alkylguanines critical for NER recognition.The exposure of DNA to alkylating agents can lead to the formation of mutagenic and toxic O⁶-alkylguanine lesions (Fig. 1A) (reviewed in ref. 1). Mutagenicity arises from mispairing with T during DNA replication, whereas toxicity is associated with mismatch repair processing of O⁶-alkylguanine:T sites. O⁶-Alkylguanine-DNA alkyltransferases (AGTs) repair many different O⁶-alkylguanine lesions by transferring the alkyl group to an active site Cys (1–4), although some are reported to be poorer substrates (5–10). Alkyltransferase-like (ATL) proteins (for reviews see refs. 3, 11, and 12) are highly homologous to AGTs but have a different amino acid (typically Trp or Ala) in place of the nucleophilic active site Cys. ATL proteins retain the ability to bind single-stranded or duplex DNA containing O⁶-alkylguanine, and although unable to undertake the de-alkylative repair reaction, they protect against the adverse effects of DNA alkylation damage by downstream recruitment of nucleotide excision repair (NER) (13–22).Open in a separate windowFig. 1.Structures of guanine, modified purines, and ODNs used in study. (A) Guanine (numbered), O⁶-alkylguanine, and modified purines incorporated into 13-mer ODN substrate (B) (X = guanine, O⁶-alkylguanine, or modified purine).In common with other proteins (including AGTs) that repair or modify DNA bases, ATL proteins use nucleotide flipping (also referred to as base flipping) to insert the target base into a tight-fitting binding pocket and thereby recognize its unique characteristics (for reviews see refs. 23–25). For ATL proteins the fidelity of this process and the formation of high-affinity complexes with cognate substrates is critical before subsequent processing by NER. Nucleotide-flipping proteins typically distinguish correct from incorrect base by using mechanisms involving steric exclusion, in which only the cognate base can access the binding site, or processes that probe the hydrogen bonding characteristics of the base. For example, in the human DNA glycosylase UDG, Tyr147 blocks access of the methyl group of T such that only U fits in the active site before its excision (26). In contrast, the human alkyladenine DNA glycosylase distinguishes between the ethenobases of A and C (Fig. S1) and the natural bases by forming a specific hydrogen bond between His136 main chain NH and the imino nitrogens (N⁶ and N⁴) of the respective ethenobases (27, 28). The bases A and C have amino groups at these positions that are hydrogen bond donors rather than acceptors, and this key interaction with His136 is therefore disrupted. Human DNA glycosylase hOGG1 distinguishes 8-oxoguanine (8-oxoG) (Fig. S1) from G by forming a hydrogen bond between the main chain carbonyl oxygen of Gly42 and the N7 proton of 8-oxoG, which is absent in G (29). The corresponding interaction with G is that of repulsion between the lone pairs on the respective positions.Somewhat paradoxically Atl1 does not have a tight-fitting pocket into which an O⁶-alkylguanine is bound. Indeed the O⁶-alkylguanine binding site is substantially larger than that found in AGT proteins (2, 16, 30, 31). This permits Atl1 to bind O⁶-alkylguanines with much bulkier alkyl groups, for example O⁶-pobG (Fig. 1A) (16). However, the mechanism by which Atl1 distinguishes between O⁶-alkylguanine and G has not been investigated, nor indeed has a comprehensive assessment of the substrate characteristics for ATL proteins been undertaken. Here we describe recognition by ATL proteins from Schizosaccharomyces pombe (Atl1) and Thermus thermophilus (TTHA1564) of oligodeoxyribonucleotides (ODNs) containing several different O⁶-alkylguanine analogs and related purines that derive from functional group modifications to the O⁶-alkylguanine structure. Both ATL proteins derive from organisms that lack an AGT protein. In comparison with processes used for base recognition by other proteins (25), our study supports an unprecedented and exquisite mechanism involving molecular readout of the electrostatic potential surface of the target base by Atl1 that permits O⁶-alkylguanine to be distinguished from G.