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Biomedical subjects

R R Freeman

Publications and source records attributed to R R Freeman.

31 records · Page 2Linked to original sources
PubMed1983

Surface antigens of malaria merozoites. A high molecular weight precursor is processed to an 83,000 mol wt form expressed on the surface of Plasmodium falciparum merozoites.

A technique was developed for obtaining high yields of naturally released Plasmodium falciparum merozoites from synchronous cultures of parasitized erythrocytes. The cultured erythrocytes were treated with trypsin to prevent reinvasion (6), and the released merozoites that accumulated extracellularly were harvested by differential centrifugation. The total biosynthetically labeled proteins of schizonts and merozoites, and those immunoprecipitated by human immune serum were analyzed and compared. The surface antigens of free merozoites, labeled by lactoperoxidase-catalyzed iodination, were also described. A monoclonal antibody, specific for a 195,000 mol wt schizont protein, and processing fragments derived from it (3) were used in immunoprecipitation and Western transfer analyses to determine which of the processing fragments are associated with merozoites and which of them are located on the merozoite surface. It was found that processing of the 195,000 mol wt precursor down to an 83,000 mol wt fragment is complete in free merozoites, and that this fragment is expressed as one of the major surface antigens of P. falciparum merozoites.

Animals↗
PubMed1983

Serological cross-reaction between high molecular weight proteins synthesized in blood schizonts of Plasmodium yoelii, Plasmodium chabaudi and Plasmodium falciparum.

A 230 000 molecular weight (MW) Plasmodium yoelii protein, a 250 000 MW P. chabaudi protein and a 195 000 MW P. falciparum protein, identified using monoclonal antibodies, have similar characteristics, and have been implicated as protective antigens. In this study the serological relationship between these proteins was investigated by Western transfer analysis. The monoclonal antibodies specific for each of the high molecular weight proteins did not cross-react with antigens of the other two parasites, but a polyvalent mouse serum raised against the purified 230 000 MW P. yoelii protein cross-reacted with the high molecular weight proteins of P. chabaudi and P. falciparum and also with the fragments derived from these proteins. This result indicates that these proteins belong to the same class of malaria parasite antigen.

Amino Acid Sequence↗
PubMed1983

Characteristics of the protective response of BALB/c mice immunized with a purified Plasmodium yoelii schizont antigen.

The response of BALB/c mice to immunization with a 230,000 mol. wt protective antigen purified from the blood stages of Plasmodium yoelii was analysed. The protective response to immunization was adjuvant-dependent, and saponin was found to be the most effective adjuvant tested. The intraperitoneal route was found to be superior to the subcutaneous route for protective immunization. Maximal protection was achieved using two immunizations with greater than 12.5 micrograms of antigen plus saponin, but even under these conditions challenge infection developed normally for 5 days, followed by the appearance of crisis forms and rapid clearance of parasites. Effective immunization induced high antibody titres, but serum from immunized mice was not protective on passive transfer. On the other hand, hyperimmune serum from mice recovered and rechallenged with live P. yoelii was protective on passive transfer, even though the titre of antibody specific for the 230,000 mol. wt antigen in this serum was the same as that in the serum from mice immunized with the purified antigen. It was concluded that the 230,000 mol. wt antigen may provide protection against P. yoelii via the cell-mediated immune effector pathway described by Playfair et al. (1979), and that hyperimmune serum contains protective antibodies specific for P. yoelii antigens other than the 230,000 mol. wt antigen.

Adjuvants, Immunologic↗
PubMed1982

Biosynthesis and processing of a Plasmodium falciparum schizont antigen recognized by immune serum and a monoclonal antibody.

Stage-specific protein synthesis by the erythrocytic forms of the malaria parasite Plasmodium falciparum was investigated by pulse labeling synchronous parasite cultures with [35S]methionine at 6-h intervals during a complete 48-h developmental cycle. About 40 labeled parasite proteins could be immunoprecipitated with human immune serum, and most of these were associated with the schizont stage of development. In particular, one schizont protein was a 195,000-mol wt species against which a murine monoclonal antibody was produced. This monoclonal antibody, 89.1 reacted with the parasite membrane in schizonts and also with the surface of free merozoites in the indirect immunofluorescence test. In addition to the 195,000-mol wt protein, antibody 89.1 immunoprecipitated a series of lower-molecular weight polypeptides from extracts of labeled asynchronous P. falciparum parasite cultures. These were shown to be related to the 195,000-mol wt protein by peptide mapping. Pulse-chase labeling of synchronized cultures, and immunoprecipitation with antibody 89.1, showed that specific processing of the 195,000-mol wt polypeptide to the lower-molecular-weight products in concomitant with schizont maturation and merozoite release. It is suggested that this P. falciparum protein may be analogous to a similarly processed 230,000-mol wt protective antigen of the rodent malaria parasite, P. yoelii.

Animals↗
PubMed1980

Protective monoclonal antibodies recognising stage-specific merozoite antigens of a rodent malaria parasite.

Immunity to malaria is mediated, at least in part, by antibody. Resistance to infection has been passively transferred with immune serum or its immunoglobulin fraction in human, simian and rodent malaria. However, because of the structural and antigenic complexity of the malaria parasites, it has proved difficult to identify and characterise those parasite antigens against which protective antibody is directed. We have produced several hybrid cell lines secreting monoclonal antibodies against the rodent malaria parasite, Plasmodium yoelii, and we now report that, of the antibodies tested, only those specific for antigens exclusive to the merozoite were protective in passive transfer experiments. Other anti-P. yoelii monoclonal antibodies, apparently recognising antigens in the membrane of the infected erythrocyte, were not protective on passive transfer. The protective monoclonal antibodies should be useful in the isolation of the important antigens of this parasite.

Animals↗
PubMed1979

Ia antigens in serum during different murine infections.

There exists in the mouse a family of I-region-controlled (Ia) antigens which carry carbohydrate-defined determinants. These antigens appear in serum as glycolipids and seem to be actively secreted by antigen-activated T-cells. This paper describes the ability of selected viral, bacterial, and protozoal infections of mice to markedly alter the serum levels of these Ia antigens. All the infectious agents examined induced substantial augmentation or suppression of serum Ia concentrations or both. Lymphocytic choriomeningitis (LCM) virus first enhanced and then suppressed serum Ia levels during the course of acute infection. Enhancement occurred during the time of ongoing virus replication and splenic lymphoproliferation while suppression coincided with the peak of the cytotoxic T-cell response and virus clearance. Listeria monocytogenes infection induced a substantial reduction in Ia levels at a time just after marked depletion of T-cells in the spleen. In contrast, Brucella abortus caused a significant increase in Ia levels 7 days postinfection, which correlates with the appearance of peak numbers of bacteria in tissues. Finally, Plasmodium yoelii, a nonlethal malarial parasite which stimulates prolonged T-cell proliferation, augmented serum Ia levels, whereas P. berghei, a lethal parasite which tends to inhibit. T-cell division, suppressed Ia secretion. Possible interpretations of these different results are presented.

Animals↗
PubMed1978

Polyclonal B-cell activation during rodent malarial infections.

The numbers of 'background' plaque-forming cells (PFC) secreting IgM specific for either sheep erythrocytes or horse erythrocytes were found to be elevated in the spleens of BALB/c mice during Plasmodium berghei and P. yoelii infection. 'Background' PFC numbers were similarly elevated in the spleens of uninfected mice injected with high speed supernatants of lysates of parasitized red blood cells. The active factor (or factors) in the supernatants was (were) non-dialysable and stable at 56 degrees C, but was (were) destroyed by heating to 100 degrees C.

Animals↗
PubMed1978

Spleen cell changes during fatal and self-limiting malarial infections of mice.

Changes in the proportions and total numbers of splenic Thy-1.2+ cells, Ig+ cells and normoblasts were analysed during fatal Plasmodium berghei and non-fatal P. yoelii infections in mice. Thy-1.2+ and Ig+ cells were identified by rosetting techniques, and normoblasts by morphological criteria. The splenomegaly observed during these infections was found to be caused mainly by proliferation of normoblasts. An early increase in the numbers of Thy-1.2+ and Ig+ cells was detected in both infections, but in P. berghei infections these responses were subsequently suppressed. In P. yoelii infections Thy-1.2+ and Ig+ cell numbers were maintained at four to five-fold above normal levels until the mice had completely recovered. During the acute phase of P. yoelii infection it appeared that most splenic T-cells expressed surface immunoglobulin.

Animals↗