Search PubMed⌕ Search

Biomedical subjects

K N Brown

Publications and source records attributed to K N Brown.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1988

Protective immunity to malaria: studies with cloned lines of Plasmodium chabaudi chabaudi in CBA/Ca mice. III. Protective and suppressive responses induced by immunization with purified antigens.

The protective effect of affinity purified antigen has been investigated in an experimental model for malaria which shows a well marked recrudescence of parasitaemia, a feature of the disease in man. A monoclonal antibody (MoAb) recognizing an epitope common to two genetically distinct cloned lines of Plasmodium chabaudi (AS and CB), was used to purify a Mr250,000 polymorphic schizont antigen (PSA) from these parasites. The purified preparations were then examined for the presence of specific and cross-reactive epitopes by immunoprecipitation with a panel of MoAb raised against P. chabaudi AS. When tested previously on smears of parasitized blood by immunofluorescence, or against lysates of parasitized erythrocytes by immunoprecipitation, most of these MoAb had been found to be AS specific. When either AS or CB affinity purified Mr250,000 PSA was used as the target, these same MoAb immunoprecipitated both antigens, and in some cases, a number of associated polypeptides (AP) which copurify with the Mr250,000 PSA. Subsequently, mice were immunized with either the purified AS or CB antigens in Freund's complete adjuvant (FCA). Prechallenge sera were compared by indirect immunofluorescence and immunoprecipitation. Sera from mice immunized with AS antigen reacted strongly with AS and cross-reacted with CB parasite preparations. Pre-challenge serum from CB antigen immunized mice reacted well with CB, but only faintly with AS preparations. In mice immunized with the AS antigen and then challenged with either AS or CB parasites, the initial parasitaemias were delayed in appearance and the height of the peak parasitaemia reduced, an effect which was most pronounced after challenge with homologous parasites. Only homologous challenge of the mice immunized with CB antigen produced statistically significant modification of the initial parasitaemia. In the immunized mice challenged with homologous parasites, the delayed appearance and slightly reduced peak of the primary parasitaemia was associated with delayed resolution of the patent parasitaemia and significant enhancement of the recrudescence.

Animals↗
PubMed1986

Protective immunity to malaria. Studies with cloned lines of Plasmodium chabaudi chabaudi and P. berghei in CBA/Ca mice. II. The effectiveness and inter- or intra-species specificity of the passive transfer of immunity with serum.

Serum was obtained from CBA/Ca mice infected, reinfected or superinfected with parasites taken one or two syringe passages from cryopreserved reference stabilates derived from cloned lines of the AS or CB isolates of P.c. chabaudi. Serum was also collected from mice superinfected with parasites derived from a cloned line of P. berghei KSP-11. When injected into normal syngeneic recipients subsequently challenged with homologous or heterologous parasites, these sera mediated some or all of the following modifications to the breakthrough parasitaemias which invariably occurred (i) an extension of the pre-patent period (ii) an extension of the time taken for the parasitaemia to reach 2% (iii) a reduction of peak parasitaemia (iv) protraction of the initial peak of parasitaemia. These modifications were particularly evident with serum from superinfected mice and to a lesser extent with serum from animals reinfected once after recovery from a primary infection. Serum taken during the course of such a primary infection produced extended pre-2% periods, other effects being only marginal. Serum mediated modifications produced by reinfection and superinfection serum appeared largely species-specific with a limited degree of cross-reactivity. Intraspecific specificity was also apparent with serum from P.c. chabaudi AS or CB reinfected or superinfected mice, although marginal cross-immunity was again observed. When analysed by the fluorescent antibody technique on smears of methanol fixed parasitized erythrocytes, reinfection and superinfection sera were almost totally cross-reactive both within and across species. Preliminary evidence that parasites breaking through the effects of these sera may constitute a phenotypic antigenic variant is presented and possible mechanisms for the parasitaemia modifying effects of the various sera discussed.

Animals↗
PubMed1985

Protective immunity to malaria: studies with cloned lines of Plasmodium chabaudi and P. berghei in CBA/Ca mice. I. The effectiveness and inter- and intra-species specificity of immunity induced by infection.

CBA/Ca mice were immunized by infection with cloned lines of Plasmodium berghei (isolates ANKA, KSP-11). Plasmodium chabaudi chabaudi (AS, CB) or Plasmodium chabaudi adami (DS) and then challenged with either homologous or heterologous parasites. Protective responses were assessed in immune mice relative to the controls by their ability to (i) extend the time taken for the mean parasitaemia to reach a predetermined level (1% or 0.1%) (ii) reduce peak parasitaemia (iii) resolve the parasitaemia sooner and/or (iv) control or eliminate recrudescences. At both the inter- and intra-species level, immunity appeared largely specific for the cloned line inducing it. At the interspecies level marginally effective cross-immunity was sometimes evident, thus P. berghei KSP-11 immune mice displayed some immunity against P.c. chabaudi AS, although immunity to this parasite was relatively ineffective against P. berghei ANKA or KSP-11. Cross-immunity was more apparent between the subspecies P.c. adami and P.c. chabaudi and between cloned lines of the latter parasite derived from the AS and CB isolates. These data reflect considerable inter- and intra-species structural and immunogenic differences in certain antigens of parasitized erythrocytes and merozoites, which have been identified in a number of murine malarias and associated with protective immunity. Similar differences recently identified in the equivalent antigens of the human parasite P. falciparum may therefore have important implications for protective immunity in man.

Animals↗
PubMed1984

A possible molecular basis for strain specific immunity to malaria.

A 250 kDa antigen implicated in the induction of protective immunity to Plasmodium chabaudi was examined with a panel of 11 monoclonal antibodies in cloned parasite lines. 2 antibodies cross-reacted with the different parasite lines while 9 were specific for one line. This antigenic diversity was correlated with major differences in one dimensional peptide maps between the purified antigen from different lines of parasites. The peptide maps also revealed some apparently conserved structure which may have been responsible for the antigenic cross reactivity. Using cloned lines of P. falciparum and a second series of monoclonal antibodies, similar antigenic and structural diversity was evident in the equivalent antigen from the important human pathogen. These findings are discussed with relationship to the induction of protective immunity to malaria.

Animals↗
PubMed1983

Maturation of the intracellular parasite and antigenicity.

The protein antigens synthesized by the malarial parasite change as the parasite matures, with a number of proteins showing strict stage-specificity. A detailed correlation between the stage-specificity of protein synthesis and parasite structure has yet to be established, but a number of proteins synthesized in the cycle are lost selectively during merozoite escape and reinvasion. These antigens are presumably associated with structures utilized and ultimately lost during this process. Particular interest has focused on some greater than 200K proteins identified as being on the surface of infected erythrocytes and internally and on the surface of merozoites. Smaller parasite proteins have also been identified in the erythrocyte membrane. The erythrocyte itself, including its membrane, is much modified by parasite growth. Changes include the presence of new cytoplasmic structures and differences in the surface labelling and isoantigenic characteristics of the surface membrane. An appreciation of the variability and specificity of exposed parasite antigens, and their relationship to newly exposed isoantigens, is central to our understanding of protective immunity to malaria.

Animals↗