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Biomedical subjects

C A Long

Publications and source records attributed to C A Long.

At least 91 records · Page 5Linked to original sources
PubMed1984

Susceptibility of CXB recombinant inbred mice to murine plasmodia.

The genetic control of susceptibility to two species of murine malarial parasites was investigated with recombinant inbred (RI) mouse strains as a model system. Initially, the nonlethal Plasmodium yoelii 17X strain was cloned by limiting dilution to minimize parasite variability. This cloned P. yoelii was used to infect C57BL and BALB/c mice, strains which are the progenitors of the CXB RI strains. Since these two strains displayed consistent differences in the kinetics of parasitemia, the seven CXB RI strains were compared for their susceptibility to the same parasite. The RI strains varied considerably when infected with P. yoelii and could be divided into susceptible and resistant groups based on mortality observed with this normally mild infection. This suggests a complex, multigenic inheritance determining susceptibility to this parasite. However, when the susceptible and resistant CXB RI mice were infected with another, unrelated plasmodial species, Plasmodium chabaudi adami, all the mice showed identical patterns of disease. Since susceptibility to different murine plasmodia does not cosegregate in the CXB RI mice, different mechanisms of resistance may be required for different plasmodial species.

Animals↗
PubMed1984

Analysis of mRNA coding for blood-stage antigens of a rodent malarial parasite, Plasmodium yoelii: mRNA coding for a possible protective antigen purify as poly A-.

We have analyzed mRNA coding for blood-stage antigens of Plasmodium yoelii by using cellfree translation of poly A+ and poly A- RNA in conjunction with immunoprecipitations. Most of the antigens recognized by mouse hyperimmune serum to P. yoelii were coded by poly A+ mRNA ranging in size from 15S to 28S. However, certain P. yoelii antigens, notably those with m.w. greater than 150 kilodaltons (kd), were coded by mRNA that purified as being poly A-. Antigens recognized by a protective monoclonal antibody (McAb) were coded by such operationally poly A- RNA. Three polypeptides apparently coded by different poly A- RNA were immunoprecipitated by this McAb. With the use of another McAb, a poly A+ mRNA of about 19S was identified as coding for a polypeptide of 46 kd synthesized in cellfree translation reactions. The same McAb recognized a 34 kd polypeptide in metabolically labeled polypeptides of P. yoelii. This antigen appeared to be processed in vivo but not in vitro. The observation that some mRNA of P. yoelii purify as being poly A- has significant implications for the construction of cDNA libraries that employ poly A+ mRNA of malarial parasites: if it applies to other species of plasmodia, some potentially important operationally poly A- mRNA may not be represented in such libraries.

Animals↗
PubMed1984

Passive immunization against murine malaria with an IgG3 monoclonal antibody.

Spleen cells of BALB/c mice that were immune to the 17X strain of P. yoelii were fused with P3X63Ag8 myeloma cells. Two hundred fifty-three of 1053 hybrid cells produced antibodies reactive with disrupted 17X parasites in a solid phase radioimmunoassay. One of these antibodies, McAb 302, reacted with the merozoites of the 17X (nonlethal) and 17XL (lethal) variants of P. yoelii. Of greater significance, McAb 302 passively protected mice against challenge infection with the lethal variant. Mice treated with this antibody before infection developed low-grade parasitemia (less than 0.3%) of short duration when challenged with P. yoelii 17XL . In contrast, control mice that had been untreated or injected with ascites fluid lacking McAb 302 uniformly died with fulminating malaria upon challenge with the same parasite. In other experiments, McAb 302 was shown capable of controlling blood parasite levels when administered to mice with patent P. yoelii 17XL infections. Although all control mice died, mice protected with a single dose of McAb 302 ultimately cleared their infections. Regardless of how passive immunization was performed, mice given McAb 302 were resistant to subsequent challenge with P. yoelii 17XL , indicating they had developed significant immunity during their initial controlled infections. McAb 302 also showed pronounced passive protective activity against the nonlethal 17X strain of P. yoelii, which is a parasite of reticulocytes. The protection afforded by McAb 302 was specific, because mice passively immunized with this antibody died when challenged with the unrelated P. vinckei. McAb 302 was shown to possess the IgG3 isotype and precipitated a 230-kd protein plus several smaller polypeptides from metabolically labeled parasite antigen preparation derived from both variants of P. yoelii. It did not react with similar preparations of other murine plasmodial species.

Animals↗
PubMed1983

Regulation of endogenous murine mammary tumor virus expression in C57BL mouse lactating mammary glands: transcription of functional mRNA with a block at the translational level.

Expression of endogenous murine mammary tumor viruses (MuMTVs) in various mouse strains is regulated in different ways, and in the absence of exogenous MuMTV, this regulation influences the incidence of spontaneous mammary tumors. Two mouse strains with low mammary tumor incidence, BALB/c and C57BL, control endogenous MuMTV expression at different stages. Neither of the strains had any detectable MuMTV polypeptides in its lactating mammary glands (LMG). However, in C57BL LMG, substantial amounts of MuMTV RNA were present, whereas very little viral RNA was detected in BALB/c LMG. By determining MuMTV RNA levels in LMG of hybrids and backcrosses of BALB/c and C57BL mice, we found that there are three unlinked, independently segregating genetic loci in C57BL mice that are responsible for the presence of moderately high amounts of MuMTV RNA in LMG. The viral RNA in C57BL LMG was processed and transported to the cytoplasm where it was found to cosediment with EDTA-sensitive polysomes. No viral proteins were detected in run-off reactions that permit completion of nascent polypeptide synthesis with polysomes from C57BL LMG, and sensitive radioimmunoassays failed to detect any MuMTV proteins in these tissues. In contrast, MuMTV mRNA purified from C57BL LMG did direct the synthesis of both gag and env MuMTV polypeptides when added to a heterologous rabbit reticulocyte lysate cell-free translation system. We propose that MuMTV mRNA in C57BL LMG, for unknown reasons, is blocked at the translational level.

Animals↗
PubMed1983

The effect of processing and storage on key enzymes, B vitamins, and lipids of mature human milk. I. Evaluation of fresh samples and effects of freezing and frozen storage.

A study was initiated to evaluate the effects of several methods of processing and storage on key enzymes, B vitamins, and lipid components of mature human milk. In order to establish standard values for the nutrient components with which to compare processed samples, a total of 30 individual raw samples of mature human milk were analyzed. There was considerable sample to sample variation as indicated by the large range of values for each component. Freezing and frozen storage had little effect on the enzymes of pooled samples of milk. Lactoperoxidase activity decreased from 36 in raw pooled samples to 17 in pooled samples slow frozen and stored for 3 months at -25 degrees C (P less than 0.05). Similarly, quick freezing and storage for 3 months significantly decreased the lactoperoxidase activity of pooled samples from 93 to 14 (P less than 0.05). Quick freezing and frozen storage tended to increase lipase activity although the changes were not significant. Freezing and frozen storage did not significantly affect the levels of biotin, niacin, and folic acid. Similarly, the total lipid fatty acid level and relative % of each fatty acid were not significantly different in the frozen samples as compared to the raw samples.

Enzymes↗
PubMed1980

Origins of the cholesterol in milk.

Studies were conducted to investigate the origin of milk cholesterol in the ruminant. In the first experiment, [1(-14)C]sodium acetate was infused into one side of the udder of a lactating goat via the test canal whereas in the second, (1,2-3H]cholesterol was injected intravenously and concurrently with a [14C]acetate intramammary infusion. In both experiments, blood and milk samples were collected at intervals for 6 days postinjection. Maximum unesterified cholesterol specific activity (sp act) in whole milk appeared at 78 hr after intravenous injections of 3H cholesterol and within 3-7 hr after infusion of [14C]acetate. Virtually all the tritium in milk was associated with unesterified cholesterol. The sp act of 14C-labeled cholesterol was only 20% of gland-synthesized decanoic acid. Decanoic acid is known to be completely synthesized in the mammary gland, and, like cholesterol, acetate is its precursor. The results indicate that, although some milk cholesterol is synthesized in the mammary gland, it is derived principally from serum cholesterol. The data show also that serum cholesterol equilibrates with membrane cholesterol of the lactating cell prior to its secretion in milk.

Acetates↗
PubMed1979

Bioactivities and the effect of dilution on various milk-borne murine mammary tumor viruses.

Infectivity titrations of milk-borne murine mammary tumor virus (MuMTV) from different sources or prepared in different ways or stored for periods of time have been compared. Titration curves were in general reproducible for MuMTVs of different sources or handled in different ways and for different methods of measurement, such as hyperplastic alveolar nodule (HAN) development, tumor development, or MuMTV antigen secretion in third-lactation milk, The curves had characteristic shapes with a low incidence of infection at low dilutions of milk, high incidences at intermediate dilutions, and low incidences at high dilutions. Infectivity incidences were unaffected by dilution over the range 10(-2) to 10(-5). The curves did not change appreciably with time of storage of milk at liquid N2 temperature for periods up to 3 years. Rate zonal fractionation of RIII milk gave zones with bioactivities which were not proportional to B-particle content. Upon dilution, the bioactivity of Zone 3, rich in B particles, and Zone 5, poor in B particles, increased, while the bioactivity of all the other zones usually decreased with dilution. The low incidence of infection at low dilutions may have been due, in part, to an immune response of the inoculated mouse. Administration of inactivated virions 4 h prior to or with MuMTV inoculations gave some evidence in support of this hypothesis but the complexity of the bioassay system for MuMTV lends uncertainty to interpretation of results.

Age Factors↗
PubMed1978

Formation of intracellular fat droplets: interrelation of newly synthesized phosphatidylcholine and triglyceride in milk.

The lipogenic system of fresh goat milk was used to investigate the relationship of lipid synthesis to formation of fat droplets. The skim milk phase was incubated with [1-carbon-14] palmitate and incorporation of activity into the glycerolipids was assayed. In two representative experiments, 44 and 56% of the label was incorporated into the lipids. Most of this activity (78 to 84%) was in triglycerides. Of 12 and 10% activity in the phospholipids, about 60% was contained in phosphatidylcholine with substantially smaller amounts in the other phospholipids. The synthesis of triglyceride and phosphatidylcholine was further investigated in relation to distribution of labeled lipids in a cream layer and a sedimenting fluff (membrane) fraction derived by centrifuging the skim milks following incubation. The correlation coefficient for the amounts of activity in phosphatidylcholine and triglyceride in the cream layer was .97. The data are consistent with synthesis of phosphatidylcholine and triglyceride to meet the requirements of surface and volume expansion, respectively, in formation of fat droplets. Our findings suggest the interesting working hypothesis that phosphatidylcholine synthesis regulates development of fat droplets.

Animals↗
PubMed1977

Role of self-carriers in the immune response and tolerance. II. Parameters of tolerance induced by haptenated lymphoid cells.

The induction of tolerance to the 2,4,6-trinitrophenyl (TNP) hapten has been studied in a system utilizing haptenated syngeneic lymphoid cells. Specific depression of the direct and indirect plaque-forming cell (PFC) responses to TNP-protein conjugates was regularly achieved by pretreatment of Lewis rats with 1 X 10(7) trinitrophenylated spleen cells or TNP lymph node cells. Very low numbers of haptenated lymphocytes were active since tolerance could be induced in vivo with as few as 10(5)-10(6) TNP spleen cells (SC). SC exposed to as little as 10-100 mug of the reactive hapten, trinitrobenzene sulfonic acid, were effective tolerogens in this system. Tolerance induced with 10(7) haptenated spleen cells persisted for at least 4 weeks. Viable intact cells did not seem to be required in this system since the cell-free supernatants from TNP-SC cultured for 24 h were also active. In addition, significant depression of an ongoing immune response could also be imposed by haptenated isologous lymphoid cells. Moderate suppression of the "hapten-specific" delayed hypersensitivity response (measured by the accumulation of 51Cr-labeled bone marrow cells) was also achieved with TNP-SC. These results suggest that haptenated isologous lymphoid cells are potent tolerogenic conjugates capable of inducing tolerance affecting antibody formation and delayed hypersensitivity. However, since we and others have shown that TNP-SC do not adversely affect the generation of hapten-specific cytotoxic T cells, it is postulated that there is a differential recognition of, or response to, hapten-modified self-carriers by functionally distinct lymphocyte subpopulations.

Animals↗
PubMed1976

Role of self-carriers in the immune response and tolerance. I. B-cell unresponsiveness and cytotoxic T-cell immunity induced by haptenated syngeneic lymphoid cells.

Normal spleen cells cultured with TNP-modified syngeneic spleen cells fail to mount an anti-TNP PFC response to TNP-ficoll or TNP-red blood cells,but go on to generate cytotoxic T cells directed at hapten-modified H-2.These results suggest that hapten-modifeid spleen cells may differentially induce B-cell tolerance and T- (Ly 2,3) cell immunity. The differential response to modified self by lymphocyte subpopulations is discussed.

Animals↗
PubMed1976

Bovine milk intake and xanthine oxidase activity in blood serum.

Xanthine oxidase activity in blood serum was measured by a sensitive radio-enzymatic assay. Pigs receiving 7.6 liters of milk daily for 100 days did not show any detectable enzymatic activity in their blood Xanthine oxidase activity in blood serum of 25 human volunteers had an average of 6.7 milliunits per liter with a range of 0 to 34.6 milliunits per liter. Neither a causal nor statistically significant relationship existed between xanthine oxidase activity in blood and average daily milk consumption, age, or sex.

Adult↗