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PubMed1993

Social support from friends and psychological distress among elderly persons: moderator effects of age.

In this study, the relationships among age, sex, friend support, and psychological distress are examined among elderly persons. Structural equation modeling and a longitudinal design are used to examine direct, indirect, and moderator (interaction) effects over a 22-month interval. Findings suggest that different causal processes operate among persons over the age of 70 (old-old) and those 50 to 70 years (young-old); the cross-lagged effects of friend support on distress and of distress on friend support are only observed in the older group. Compared to the young-old, the old-old receive less friend support at time 2 (T2) if they experienced psychological distress at time 1 (T1), and the old-old are more distressed at T2 if they received low levels of support at T1. As a result of this age interaction, the total effects of sex on distress and support at T2 are twice as large in the sample of old-old persons as in the sample of young-old persons. Such findings suggest that the old-old in general and old-old men in particular are especially vulnerable to psychological distress when losing friend support, and to lose friend support when experiencing psychological distress. Implications of these and other findings are discussed.

Age Factors↗
PubMed1986

Induction of differentiation in Friend erythroleukemia cells with dimethyl sulfoxide, hexamethylene bisacetamide and sodium butyrate is not accompanied by changes in proviral DNA or its expression.

The integration pattern, copy number and DNA expression of the Friend virus genome was examined in Friend erythroleukemia cells induced to differentiate with dimethyl sulfoxide, hexamethylene bisacetamide and sodium butyrate. The integrated proviral DNA in Friend erythroleukemia cells was examined by Southern hybridization with a cloned Friend virus (F-MuLV) probe at days 1 and 4 following inducer treatment, as well as on day 6 at which time the cells had remained for 48 h in inducer free medium. KpnI fragments 9 and 5.7 kb long were observed. The copy number of each fragment remained constant throughout the erythroid differentiation process. EcoRI digestion of DNA isolated from cells at different times following the inducer treatment demonstrated multiple integration sites of the proviral genome, which also remained constant during the differentiation process. Proviral DNA expression was examined at 4 h and 4 days following inducer treatment as well as on day 6 by which time cells remained for 48 h in inducer free medium. Northern blot hybridization to the F-MuLV probe indicated no change in the provirus gene expression independent of the class of inducers. These observations reinforce our conclusions that the viral genome and its transcription product do not play a major role in the differentiation process of Friend erythroleukemic cells.

Acetamides↗
PubMed1975

Helper specificity for retrieval of defective friend virus.

A Friend virus-induced reticulum-cell sarcoma from BALB/c mice has been cultivated in vitro in our laboratory for more than 11 years and contains no detectable evidence of virus. However, Friend virus could be retrieved readily from the tissue cultures by any of several lymphatic leukemia viruses belonging to the Friend-Moloney-Rauscher (FMR) group, as long as the helper viruses were actively replicating in a culture. Helper activity appeared to be highly specific and limited to the FMR group including the B-tropic Tennant leukemia virus which produced a B-tropic Friend virus pseudotype. The naturally occurring type AKR murine leukemia viruses and the related Gross passage A virus failed both in vivo and in vitro to retrieve the Friend virus genome from the virus-free tumor cells.

Animals↗
PubMed1980

Phorbol ester tumor promoters block the transition from the early to the heme-dependent late program of Friend cell differentiation.

In this study, the mechanism of inhibition of differentiation of Friend erythroleukemia cells by the phorbol ester tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), has been examined. These studies indicate that some early events associated with Friend cell differentiation, including an early change in 86Rb+ transport and a decrease in cell volume, still occur in the presence of TPA. However, several late events in the program of Friend cell differentiation, including the induction of heme synthesis and the loss of proliferative capacity, are inhibited by TPA. These effects of TPA can be reversed by hemin, which alone does not induce Friend cells to differentiate. The addition of hemin to cultures grown in the presence of inducer plus TPA for several days results in the rapid restoration of hemoglobin synthesis, and also causes a parallel decrease in colony-forming ability. These results suggest that tumor promoters may inhibit only heme-dependent events, rather than the entire program of Friend cell differentiation.

Animals↗
PubMed2006

The interactive influences of friend deviance and reward dominance on the development of externalizing behavior during middle adolescence.

This study investigated the interactive effects of friend deviance and reward dominance on the development of externalizing behavior of adolescents in the Child Development Project. Reward dominance was assessed at age 16 by performance on a computer-presented card-playing game in which participants had the choice of either continuing or discontinuing the game as the likelihood of reward decreased and the likelihood of punishment increased. At ages 14 and 16, friend deviance and externalizing behavior were assessed through self-report. As expected, based on motivational balance and response modulation theories, path analysis revealed that age 14 friend deviance predicted age 16 externalizing behavior controlling for age 14 externalizing behavior. Reward dominance was a significant moderator of the relationship between friend deviance and externalizing behavior. The contributions of deviant friends to the development of externalizing behavior were enhanced by adolescents' reward dominance.

Adolescent↗
PubMed1983

Isolation and characterization of plasma membranes from Friend erythroleukaemic cells. A study with sphingomyelinase C.

Plasma membranes have been prepared from Friend erythroleukaemic cells using a Dounce homogenization technique followed by differential and sucrose gradient centrifugations. (I) A plasma membrane fraction was obtained which showed a 20- to 30-fold enrichment in 5'-nucleotidase, alkaline phosphodiesterase I, alkaline phosphatase and in 32P-labeled (poly)phosphoinositides. About 1% of the total protein, 6-7% of phospholipid, 8-9% of cholesterol and 12-15% of each of the above markers were recovered in the plasma membrane fraction with an average yield of 15-20%. The plasma membrane was characterized by a high cholesterol to phospholipid molar ratio (0.626), a 2-fold enrichment in sphingomyelin and in phosphatidylserine as compared to the whole cell and by the complete absence of diphosphatidylglycerol. (2) When compared to the phospholipid composition of the mature mouse erythrocyte membrane, the plasma membrane of the Friend cell only differs by a higher phosphatidylcholine and a lower phosphatidylethanolamine content, whereas the levels of sphingomyelin and phosphatidylinositol plus phosphatidylserine are similar. (3) Friend cells were treated with sphingomyelinase C (S. aureus) under non-lytic conditions and subsequently submitted to subcellular fractionation. The results showed that the plasma membrane accounted for 38.5% of the total phospholipid, 64.1% of the total cholesterol and about 4.4% of the total protein content of Friend cells. (4) Sphingomyelin appeared to be asymmetrically distributed in the plasma membrane of Friend cells, with about 85% of this phospholipid being present in the outer monolayer.

Animals↗
PubMed2005

Friends in the 'hood: Should peer-based health promotion programs target nonschool friendship networks?

PURPOSE: To examine the characteristics of inner city African-American adolescents nonschool-based and school-based friendship networks and to explore the influence of these networks on health risk behavior. METHODS: We assessed close friendships networks in a probability sample of inner city African-American youth living in a single neighborhood and describe the networks and health risk behavior of network members. The initial probability sample was obtained via telephone (Random Digit Dialing [RDD] sampling) and followed up with in-person interviews with telephone respondents (seeds). Subsequently, seeds' friends were recruited and completed an in-person interview. RESULTS: A majority of friendship networks included some nonschool friends (57%) and 24% of networks were composed exclusively of nonschool friends. As expected, youth were more likely to spend time with school-based friends on weekdays. On weekends, youth were equally likely to spend time with both school and nonschool networks. Youth in the same friendship group tended to engage in similar behaviors. Health risk behaviors were high regardless of whether networks were nonschool based, mixed, or school based. CONCLUSIONS: The high proportion of nonschool friendships suggests that out-of-school networks may be an important influence in this population. Youth spend time with their friends, regardless of network type, on weekends, and weekends are a high-risk period for health-damaging behaviors. Levels of experience with health risk behaviors suggest that both school and nonschool environments require intervention. Future social influence prevention efforts that are broad-based are likely to have maximal impact.

Adolescent↗
PubMed2005

The role of social norms and friends' influences on unhealthy weight-control behaviors among adolescent girls.

Dieting is common among adolescent girls and may place them at risk of using unhealthy weight-control behaviors (UWCBs), such as self-induced vomiting, laxatives, diet pills, or fasting. Research has suggested that social factors, including friends and broader cultural norms, may be associated with UWCBs. The present study examines the relationship between the school-wide prevalence of current weight loss efforts among adolescent girls, friends' dieting behavior, and UWCBs, and investigates differences in these associations across weight categories. Survey data were collected in 31 middle and high schools in ethnically and socio-economically diverse communities in Minnesota, USA. The response rate was 81.5%. Rates of UWCBs were compared across the spectrum of prevalence of trying to lose weight and friends' involvement with dieting, using chi(2) analysis and multivariate logistic regression, controlling for demographic factors and clustering by school. Girls with higher body mass index (BMI) were more likely to engage in UWCBs than those of lower BMI. Multivariate models indicated that friends' dieting behavior was significantly associated with UWCBs for average weight girls (OR = 1.57, CI = 1.40-1.77) and moderately overweight girls (OR = 1.47, CI = 1.19-1.82). The school-wide prevalence of trying to lose weight was significantly, albeit modestly, related to UWCBs for average weight girls (15th-85th percentile; OR = 1.17, CI = 1.01-1.36), and marginally associated for modestly overweight girls (85th-95th percentile; OR = 1.21, CI = .97-1.50), even after controlling for friends' dieting behaviors. The social influences examined here were not associated with UWCBs among underweight ( < 15th percentile) or overweight ( > 95th percentile) girls. Findings suggest that social norms, particularly from within one's peer group, but also at the larger school level may influence UWCBs, particularly for average weight girls. Implications for school-based interventions to reduce UWCBs are discussed.

Adolescent↗
PubMed2005

Preschool children's interactions with friends and older siblings: relationship specificity and joint contributions to problem behavior.

The primary aim of the present study was to examine the extent to which friend and sibling relationship quality jointly contribute to children's behavioral adjustment. Preschool-aged children (N = 52) were observed separately with a friend and an older sibling during a free-play session and a sharing task. Mean comparisons indicated that friendship dyads, on average, engaged in more complex social play and more intense conflict (but only during free play), whereas sibling dyads were characterized by greater asymmetry. Few friend-sibling associations emerged. Friend and sibling relationship quality in the sharing task together accounted for a significant portion of variance in parent-reported aggressive-disruptive behavior, and a Sibling x Friend interaction indicated that greater relationship quality with one partner buffered children from poor behavioral adjustment when relationship quality with the other partner was low or moderate. Implications for preventive intervention efforts are discussed.

Adaptation, Psychological↗
PubMed2003

Family or friends: who plays a greater supportive role for Latino college students?

This study compared the relative contribution of perceived family and friend support to psychological well-being and distress and examined whether family or friend support moderated the effects of stress on psychological adjustment in 338 Latino (228 Mexican American, 110 Central American) college students from a predominantly Latino university. Two multiple regressions, controlling for gender, socioeconomic level, acculturation level, and stresses (generic college, acculturative, and minority status), showed that friend support made a slightly greater contribution to well-being than family support, and friend support and not family support protected against psychological distress. Neither family nor friend support moderated the effects of stress on psychological adjustment. Further examination of these variables that assess common-specific stresses within a culture-specific theoretical framework is recommended.

Acculturation↗
PubMed1973

Host restriction of Friend leukemia virus. Role of the viral outer coat.

Host restriction of oncogenesis of RNA tumor viruses in vivo is associated with several gene loci. One of these genes, the Fv-1 locus in mice, is expressed in vitro and may be studied in mouse-embryo cultures that are restrictive or permissive for replication of Friend leukemia virus. Two strains of Friend leukemia virus, N-or B-tropic, show reciprocal ability to replicate successfully in either NIH Swiss (N-type) or BALB/c (B-type) cells that differ at the Fv-1 locus. These two strains of virus and two cell lines form a system to measure host restriction in vitro. Measurement of adsorption of Friend leukemia virus to permissive or restrictive cells reveals no difference in rate or total amount of virus bound. Furthermore, studies with virions of vesicular stomatitis virus phenotypically mixed within an envelope containing Friend leukemia virus protein show no differences in penetration or replication of vesicular stomatitis virus. These results strongly suggest that host restriction of Friend leukemia virus is due to an intracellular event in the viral replication cycle.

Animals↗
PubMed1981

Quantitative colony method for tumorigenic cells transformed by two distinct strains of Friend leukemia virus.

An in vitro colony method capable of detecting spleen cells malignantly transformed by Friend leukemia virus is described. These colony-forming cells, which form large erythroid colonies (10(4)-10(5) cells) in methylcellulose, can be detected late after infection with either the anemia-inducing (FV-A) or polycythemia-inducing (FV-P) isolates of Friend virus. Colony formation by these cells is dependent only on fetal calf serum as an exogeneous growth factor. The presence of these colony-forming cells in FV-P-infected spleens could not be detected until at least 3 weeks after virus infection, even though the most rapid increase in spleen weight occurred earlier, between 1 and 2 weeks after infection. Thereafter, the numbers of colony-forming cells increased sharply up to 5 weeks after infection with FV-P, beyond which time the mice generally did not survive. After infection with FV-A, colony-forming cells were detected only at 8-12 weeks and their numbers generally increased thereafter. Permanent cell lines were established from a significant fraction of FV-P and FV-A-induced colonies, and these cell lines could be chemically induced to synthesize hemoglobin. All individual colonies produced complete Friend virus complex. However, virus production appeared to decline in at least some cell lines. Both FV-P- and FV-A-induced colonies contained cells capable of forming spleen colonies in irradiated recipients and subcutaneous tumors in unirradiated mice. Thus, the assay method described here appears to detect a unique class of malignant Friend virus-transformed cells that can be detected only in the advanced stages of Friend virus-induced erythroleukemia.

Animals↗
PubMed2002

Verbal and nonverbal interactions of four- and five-year-old friends in potential conflict situations.

Dyads of 4- and 5-year-old friends and nonfriends attending preschools in central Italy were identified by friendship nominations. The 217 dyads of friends and non-friends participated in 2 closed-field tasks designed to simulate real-life situations of potential conflict. In the 4-year-old cohort, there were no significant differences in the behavior of the partners in either of the situations. However, at age 5 years, friends respected the rules of a fast-paced competitive game significantly more than did nonfriends. In discussing how to share a single object (a chocolate egg with a toy inside), 5-year-old friends were more likely to reach agreement than were nonfriends. The results suggest important developmental changes in the processes of negotiation and sharing within the preschool years.

Child Behavior↗
PubMed2004

The role of close friends in African American adolescents' dating and sexual behavior.

This study examined the role of close friends in the sexual lives of African American adolescents. Fifteen African American adolescents residing in an urban neighborhood participated in individual in-depth qualitative interviews. The findings suggest that close friends play a critical role in the dating and sexual behaviors of inner-city African American adolescents, as they appear to serve as socializing agents that impact how adolescents conceptualize and socially construct dating and sexual roles and behaviors. Close friends also play a significant role in acquiring new dating and sexual partners and in determining the course of dating and sexual relationships. Although females and males expressed similar expectations regarding sexual fidelity and condom use, they differed with regard to their method and process of talking with friends about dating and sex, their shared social constructions about dating and sexual roles and expectations, and their perceptions of the meaning of dating. We discuss the implications of the findings in terms of involving close friends in interventions focused on improving the sexual health of African American adolescents. Future directions for research with African American adolescents and sexuality are also discussed.

Adolescent↗
PubMed1972

A classification of the murine leukemia viruses. Neutralization of pseudotypes of Friend spleen focus-forming virus by type-specific murine antisera.

Coinfection of neonatal BALB/c mice with helper-dependent Friend spleen focus-forming virus (SFFV), as contained in the Friend virus (FV) complex, and antigenically distinct Moloney leukemia virus (MolLV) resulted in the recovery of a MolLV pseudotype of SFFV, abbreviated SFFV(MolLV). The antigenic alteration of SFFV was observed by following its neutralization kinetics in vitro by specific Friend or Moloney typing antiserum. Effective pseudotype production was accomplished only when N-tropic LLV-F (the natural helper virus in the FV complex) was inhibited in B-type mice coinfected with an NB-tropic MolLV or other murine leukemia virus (MuLV) preparation. SFFV pseudotypes could not be prepared by using murine viruses other than leukemia viruses. SFFV prepared after two serial passages in the presence of MolLV was effectively neutralized by Moloney antiserum, but not by Friend typing antiserum; therefore, the envelope of the pseudotype virus, SFFV(MolLV), is homogeneous. Pseudotype virus was antigenically stable in the absence of continued mixed infection of BALB/c mice with SFFV(MolLV) and MolLV. However, SFFV(MolLV) was easily converted back to the LLV-F type after only one passage in BALB/c mice coinfected with NB-tropic LLV-F. The antigenic interconversion between LLV-F and MolLV types demonstrated that SFFV is defective with respect to the expression of neutralizable envelope antigens. Analysis of the neutralizable envelope antigens of nine SFFV(MuLV) pseudotypes by a panel of seven typing antisera made possible a "type-specific" SFFV(MuLV) envelope classification. Two major categories have been identified which correspond to the Gross (G) and Friend-Moloney-Rauscher (FMR) subgroups. Further, the FMR subgroup was divided into four types on the basis of distinct neutralization patterns. These results indicated that the specificity observed by cytotoxic G vs. FMR antisera is different from that observed by neutralization kinetics. We therefore suggest that the specific antigens revealed by virus neutralization tests be referred to as type specific.

Animals↗
PubMed1978

Helper-independent mink cell focus-inducing strains of Friend murine type-C virus: potential relationship to the origin of replication-defective spleen focus-forming virus.

Recent studies have indicated that both the replication-defective spleen focus-forming virus (SFFV) in the Friend virus complex and the helper-independent mink cell focus-inducing (MCF) viruses derived from AKR-murine leukemia virus (MuLV) are env gene recombinants between ecotropic virus and xenotropic virus. In an attempt to isolate additional env gene recombinants between Friend murine leukemia virus (F-MuLV) and xenotropic virus, we have inoculated cloned ecotropic F-MuLV into newborn NIH Swiss mice and analyzed MuLV released from preleukemic and leukemic spleens of infected mice. Two helper-independent MCF strains of F-MuLV have been isolated. Like the previously described AKR-MCF viruses, the Friend MCF viruses are env gene recombinants between an ecotropic virus (F-MuLV) and a mouse xenotropic virus, as shown by host range, interference pattern, and tryptic peptide analysis of the gp70s of these MuLV. Furthermore, RNA from the Friend MCF viruses hybridizes completely to cDNAsffv, a nucleic acid probe which detects that portion of SFFV which was not derived from P-MuLV. The ability to isolate replicating MCF viruses derived from F-MuLV FURTHER strengthens the parallels between the Friend erythroleukemia system and the AKR thymic leukemia system. Finally, the potential relationship of helper-independent env gene recombinants between F-MuLV and xenotropic virus to be highly leukemogenic SFFV is discussed.

AKR murine leukemia virus↗
PubMed1980

Anemia- and polycythemia-inducing isolates of Friend spleen focus-forming virus. Biological and molecular evidence for two distinct viral genomes.

Two distinct clones of Friend spleen focus-forming virus (SFFV), differing in their erythroleukemic potential, are described. These isolates have been cloned free of their associated helper viruses and shown to be replication-defective. Both SFFV isolates have been rescued from rat fibroblast nonproducer cell clones with cloned replication-competent viruses, F-MuLVA and F-MuLVP, obtained from the anemia- or polycythemia-inducing isolates of Friend virus complex, respectively. These rescued viruses induce a rapid proliferative disease associated with the appearance of macroscopic spleen foci and splenomegaly. In addition, each is subject to regulation by the W, Steel (Sl), and Fv-2 host gene loci. These two isolates of SFFV can, however, be distinguished by both biological and molecular criteria. Friend SFFVP induces a rapid polycythemia associated with the appearance of large numbers of erythropoietin (EPO)-independent erythroid colony-forming cells in the marrow and spleen. In contrast, SFFVA induces a rapid anemia associated with a progressive decrease in the number of EPO-dependent erythroid colony-forming cells in marrow, and a rapid increase in the number of EPO-dependent erythroid colony-forming cells in spleen. Furthermore, the nature of the disease induced by the two isolates of SFFV is independent of the Friend helper virus: SFFVP, rescued from a nonproducer cell clone with either F-MuLVA or F0MuLVP, induced a polycythemic transformation, whereas SFFVA, rescued with either F-MuLVA or F-MuLVP, induced an anemic transformation. The two Friend SFFV isolates can also be discriminated on the basis of translational products encoded by their gag and env genes: SFFVP encodes the amino-terminal gag-gene protein p15, whereas SFFVA encodes the gag-gene proteins p15, p12, and p30. In addition, the SFFV isolates encode nonidentical 55,000-mol wt env gene-related proteins that can be distinguished by analysis of their methionine-containing tryptic peptides.

Anemia↗
PubMed1976

Friend spleen focus-forming virus production in vitro by a nonerythroid cell line.

We developed a cell line (IS) that continuously produced both Friend spleen focus-forming virus (SFFV) and XC plaque-forming virus in vitro. The line was derived from the enlarged spleen of an inbred SIM mouse previously infected with a polycythemic strain of Friend leukemia virus in vivo. Friend SFFV titers of 10(4) spleen focus-forming units/ml of culture medium were maintained for more than 200 cell generations. The virus from IS cells induced the splenomegaly and high hematocrit typical of Friend virus-induced erythroid disease in SIM mice. Cells of the IS line were adherent and phagocytic and had a low saturation density. They produced no tumors after being injected sc into normal syngeneic hosts and no spleen colonies after being injected iv into supralethally irradiated hosts. IS cells did not have the character of erythroid cells: They did not contain detectable heme as measured by benzidine-peroxide reagent, did not contain globin mRNA in detectable amounts, and did not produce erythroid colonies in plasma culture in the absence or presence of erythropoietin. According to these criteria, growth in the presence of dimethyl sulfoxide did not stimulate erythroid differentiation of IS cells. We concluded that Friend SFFV can infect nonerythroid spleen cells but that replication of the virus was not obligatorily coupled to expression of genes associated with the erythroid phenotype.

Animals↗