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Biomedical subjects

K N Brown

Publications and source records attributed to K N Brown.

At least 19 recordsLinked to original sources
PubMed1992

Identification and quantification of rodent malaria strains and species using gene probes.

A DNA probe PCsv4 and a subclone thereof PCsv4.1, hybridize specifically to rodent malaria DNA. DNA purified from a small volume (10 microliters) of infected mouse blood was used to determine the composition of the parasite population present. The hybridization signal following PCsv4 probing of slot-blotted DNA correlated directly with parasitaemia. The hybridization pattern and intensity, resulting from probing restriction enzyme digested and Southern-blotted genomic DNA, determined the identity of the infecting parasite line(s), and provided a semi-quantitative measure of parasite burden. Fifteen parasite lines representative of all four Plasmodium species infecting rodents can be differentiated in this way.

Animals↗
PubMed1992

Assessment of parasite population dynamics in mixed infections of rodent plasmodia.

Cloned lines of the four rodent Plasmodium species can be differentiated by the RFLP pattern generated following Southern blotting and probing with PCsv4.1, a probe derived from a P. chabaudi chabaudi genomic library. Groups of CBA/Ca mice were inoculated simultaneously with cloned lines from two parasite species or strains. Six mixed species and three mixed strain infections using rodent malaria lines were initiated. The composition of the parasite population in each group was determined qualitatively and semi-quantitatively by analysis of the DNA purified from daily blood samples, thereby providing a dynamic representation of each mixed infection. Effects on the course of parasitaemias are presented and discussed.

Animals↗
PubMed1991

In vivo effects of anti-idiotype on Plasmodium chabaudi infection in mice.

A polyclonal anti-idiotype was raised in rabbits following immunization with a murine monoclonal antibody which recognized a 250,000 MW antigen of Plasmodium chabaudi-infected erythrocytes. The monoclonal antibody, NIMP M23 (clone 3,) has been shown to protect mice against homologous parasite challenge. Following purification, the anti-idiotype was shown to bind only the immunizing idiotype and to recognize antigen-binding site-associated anti-idiotype. Mice primed with anti-idiotype and challenged with live parasites had an altered course of infection, with significant reduction in their peak parasitaemia levels. Anti-idiotype priming did not induce an antigen-reactive antibody response in vivo but a population of T cells capable of proliferating in vitro to P. chaubaudi-infected red cells was stimulated. These data are discussed in the context of possible idiotypic interaction in murine malaria.

Animals↗
PubMed1991

The 235 kD rhoptry protein of Plasmodium yoelii.

A 235 kD rhoptry protein produced by the malaria parasite, Plasmodium yoelii is the target of antibodies that protect mice against blood-stage challenge with the virulent YM strain. In the protected animals the parasites are confined to reticulocytes and the course of parasitaemia is reminiscent of an avirulent 17X strain infection. The DNA coding for the rhoptry protein has been identified as a multigene family containing at least four members. Sequence analysis of short DNA clones has identified the C-terminus of the protein; a preliminary analysis of longer clones confirms that the genes are polymorphic. The possible implications of these findings for the biology of the parasite are discussed.

Amino Acid Sequence↗
PubMed1991

Protective immune responses as indicators of antigenic diversity and stability.

By definition, the biology of a living organism must be characterized before its molecular biology can be interpreted. Malariologists are fortunate in that the malaria parasite was used as a well-controlled therapy for tens of thousands of hospital patients. During many of these treatments the opportunity was taken to study malaria and the behaviour of the parasite in detail. From these, and similar studies on volunteers, together with numerous epidemiological surveys, the operational characteristics of immunity to malaria in man have been well defined. Unfortunately this information, which exists in some detail in the older literature, does not seem to have been available to many investigators. This situation has led to interpretations of molecular data which are inconsistent with the known biology of the parasites and human-parasite relationships. This article considers how the structure of one of the best studied antigens, MSP1, can be viewed in the context of the host-parasite relationship. It postulates some testable hypotheses which aim to reconcile the molecular characteristics of the antigen with the biology and immunology of the asexual erythrocytic stage of the parasite.

Animals↗
PubMed1990

The parasitology of malaria and the study of protective immunity.

Phenotypic antigenic variation within parasite strains and antigenic diversity between strains are important parameters in understanding the development of immunity to malaria. With the Plasmodium chabaudi chabaudi model in inbred mice, a combination of serological tests and DNA technology can be used to study the specificity of inducer and effector mechanisms in an infection with characteristics similar in many ways to those of P. falciparum in man.

Animals↗
PubMed1990

The adoptive transfer of T-cell dependent immunity to Plasmodium chabaudi chabaudi in CBA/Ca mice is achieved only after superinfection of immune spleen cell donors.

The transfer of spleen cells from CBA/Ca mice recovered from a P. c. chabaudi AS primary infection into irradiated syngeneic recipients conferred very poor protection. Neither elimination of Ly2 cells from immune spleen cells nor reinfection of the donors some days before transfer improved protection significantly. Significant protection was transferred with spleen cells from donors which had been infected 7 times prior to cell transfer. Transferred protection was reduced or eliminated by pretreatment of cells with anti-Thy-1 or anti-L3T4 monoclonal antibodies but not with anti-Ly2.

Animals↗
PubMed1989

The use of a DNA probe for the differentiation of rodent malaria strains and species.

A clone, PCsv4, derived from a partial genomic library of the rodent malaria Plasmodium chabaudi chabaudi AS strain, contains an insert which when used as a probe at low stringency in Southern blotting of genomic DNA from a variety of strains, subspecies and species of rodent malaria parasites, results in a pattern of hybridisation which is specific to each of the DNA samples used, thus providing an accurate method to define a rodent malaria line. The insert only hybridises to DNA derived from malaria parasites of rodent species. The insert also hybridises to a small number of RNA transcripts.

Animals↗
PubMed1989

Use of a DNA probe to analyse the dynamics of infection with rodent malaria parasites confirms that parasite clearance during crisis is predominantly strain- and species-specific.

A DNA probe, PCsv4.1, isolated from Plasmodium chabaudi chabaudi AS, generates in Southern blotting experiments restriction fragment length polymorphisms specific to a particular rodent malaria parasite line. It was used to develop an assay which allows identification and semi-quantitative compositional analysis of sample parasite populations in which one or more strains, subspecies or species were present. In experiments where mechanisms effecting parasite clearance during crisis were studied, the assay was used to determine the composition of parasite populations present in P. c. chabaudi AS infected mice challenged during crisis with homologous or heterologous parasites. It was thus confirmed that clearance mechanisms during crisis operate in a predominantly specific manner.

Animals↗
PubMed1989

Invasion of mature and immature erythrocytes of CBA/Ca mice by a cloned line of Plasmodium chabaudi chabaudi.

During the early stages of the primary Plasmodium chabaudi chabaudi AS parasitaemia in CBA/Ca mice this parasite invaded normocytes, but as the parasitaemia developed increasing numbers of parasites were seen within reticulocytes. During and just after peak parasitaemia, as further parasite replication was controlled, the 'crisis' phase ensued, mice became increasingly anaemic and reticulocyte numbers were markedly increased. As the parasitaemia was resolved during crisis in excess of 25% of parasites had invaded reticulocytes. In phenylhydrazine-pretreated mice with artificially high reticulocyte levels and infected with P.c. chabaudi AS, normocyte/reticulocyte invasion occurred with equal frequency. No reduction in the infectivity of parasite populations developing in reticulocytes was observed.

Anemia↗
PubMed1989

Protective immunity to malaria: studies with cloned lines of rodent malaria in CBA/Ca mice. IV. The specificity of mechanisms resulting in crisis and resolution of the primary acute phase parasitaemia of Plasmodium chabaudi chabaudi and P. yoelii yoelii.

Low numbers of parasites from cloned lines of the rodent malaria parasites, Plasmodium chabaudi chabaudi AS and P. yoelii yoelii A, injected into CBA/Ca mice produce acute but usually self-limiting infections. During crisis, i.e. 1-2 days after peak parasitaemia, 'pre-immune' mice experiencing such 'background' infections were reinfected intravenously with homologous parasites or parasites of heterologous strains or species. P. c. chabaudi AS pre-immune mice controlled an AS challenge with essentially the same kinetics as the background infection. Reinfection of AS pre-immune mice with the heterologous (CB and IP-PCI) P. c. chabaudi strains or P. chabaudi adami DS had little effect on the initial growth of these parasites, although eventually the parasitaemia was controlled. In contrast, a partial inhibitory effect on the growth of P. vinckei lentum DS was evident. Challenge with the non-lethal (A) or lethal (YM) variants of P. y. yoelii resulted in an increase in both the growth and virulence of these parasites. P. y. yoelii A pre-immune mice controlled a homologous challenge, but were less effective at controlling the YM variant. In addition, they were unable to clear rapidly a P. c. chabaudi AS or P. v. lentum DS challenge. Both the multiplication and virulence of P. berghei ANKA were enhanced. These findings demonstrate that resolution of the primary acute parasitaemia in P. c. chabaudi AS- and P. y. yoelii A-infected mice is predominantly mediated by species- and strain-specific mechanisms.

Animals↗
PubMed1989

In vivo selection of populations of Plasmodium chabaudi chabaudi AS resistant to a monoclonal antibody that reacts with the precursor to the major merozoite surface antigen.

Mice bearing a hybridoma secreting a monoclonal antibody (MAb), MAb-3, which significantly delays the onset of a Plasmodium chabaudi chabaudi AS, but not P. chabaudi chabaudi CB, challenge parasitemia in a passive transfer assay and which is specific for the precursor to the major merozoite surface antigen (PMMSA) of P. chabaudi chabaudi AS, were challenged intravenously with 10(3) P. chabaudi chabaudi AS-parasitized erythrocytes. The resultant parasitemia was very similar to that in normal mice except that initially the parasitemia was sometimes slightly delayed. Parasites derived from cryopreserved stabilates isolated from MAb-3 hybridoma mice with an unmodified parasitemia, or with a delayed parasitemia, were found to have lost their susceptibility to MAb-3 in the passive transfer assay. A number of anti-PMMSA MAb were used to immunoprecipitate lysates of parasite populations isolated directly from hybridoma-bearing mice. In some instances and with certain of the MAb, immunoprecipitation patterns were modified, but other isolates were not detectably different when compared with unselected P. chabaudi chabaudi AS parasites. Using a panel of MAb reacting with the PMMSA of P. chabaudi chabaudi AS, immunoprecipitation patterns of parasites derived from cryopreserved stabilates isolated from hybridoma-bearing mice were determined at 2-h intervals through the appropriate part of the parasite maturation cycle. In these derived populations, resistance to MAb-3 was not associated with a change in the immunoprecipitation reaction with the MAb used. These results are discussed in the context of current knowledge of genotypic and phenotypic antigenic diversity of malaria parasites and other protozoa.

Animals↗
PubMed1988

Cloning of genomic fragment from Plasmodium chabaudi expressing a 105 kilodalton antigen epitope.

The 105 kDa antigen of Plasmodium chabaudi has many characteristics of the P. falciparum Pf 155 (RESA) molecule. A clone (pPC105e) from a P. chabaudi genomic library was isolated using immune screening with a 105 kDa antigen specific monoclonal antibody (B7E10). Southern, Northern and Western blotting analyses provide evidence for a lack of variability at the protein and DNA levels. A subclone of the insert in the expression vector pEX2, synthesises a fusion peptide which contains the epitope recognized by B7E10. Sequences homologous to the insert were detected in the genome of three other rodent and two primate malarias.

Animals↗
PubMed1979

Morphological stabilization of capsules of group B streptococci, types Ia, Ib, II, and III, with specific antibody.

Antibody prepared to the type-specific capsular polysaccharides of group B streptococci was used to demonstrate a stabilizing effect on the capsular glycocalyx. This permitted visualization by electron microscopy of the size of the capsule relative to the rest of the bacterial cell, and clear differences in the dimensions of untreated and antibody-treated capsular material were noted. Antibodies produced against group B streptococci types Ia, Ib, II, and III were used to demonstrate morphologically that the organization and extent of the capsular glycocalyx more closely resembles its natural state on stabilization by reaction with specific antibody.

Animals↗
PubMed1979

The possible role of isoantigens in protective immunity to malaria.

The possibility that autoimmune responses to modified red cell antigens might be involved in protective immunity to malaria was investigated in Plasmodium berghei infection of August rats. Animals rendered anaemic by phenylhydrazine treatment at the time of immunization showed significantly greater protection than rats given antigen alone, or phenylhydrazine alone. Adoptive transfer experiments indicated that this enhanced response could be transferred with spleen cells.

Animals↗
PubMed1979

Synthesis of Plasmodium knowlesi polypeptides in a cell-free system.

Preliminary results are presented concerning the characterization of Plasmodium knowlesi antigens. RNA with messenger activity has been extracted from P. knowlesi and translated in a rabbit reticulocyte cell-free system. The products of this system have been analysed both before and after precipitation with specific P. knowlesi antiserum and many polypeptides ranging in molecular weight from over 100 000 to approximately 20 000 have been found. A good correlation was found between these results and those obtained by McColin with in vitro labelling of P. knowlesi with ((3)H)-isoleucine. The major polypeptide in both systems had a molecular weight of about 50 000-55 000. These results indicate the parasite origin of the antigens.

Animals↗