Pathogenicity of Theileria parva is influenced by the host cell type infected by the parasite
Summary (2 min read)
MATERIALS AND METHODS
- The animals were produced on the International Livestock Research Institute ranch, which is free of T. parva, and were reared indoors under parasite-free conditions from 4 to 5 days of age.
- The level of infection in each batch of ticks was estimated by counting the number of infected acini in a sample of dissected salivary glands stained with methyl green pyronine.
- Purified populations of B cells and T cells were obtained by indirect immunofluorescence staining of PBMC with specific monoclonal antibodies (MAbs) and then by sorting of positive cells on a FACStar Plus cell sorter (Becton Dickinson, Mountain View, Calif.).
- In each experiment, a sample of sorted cells was checked for purity and if necessary the cells were subjected to a second round of sorting.
Infection of cells with T. parva.
- Infected tick salivary glands were suspended in the same medium and ground in a glass tissue grinder at room temperature.
- To obtain cloned infected cell lines, cells were distributed at limiting dilutions ranging from 10 3 cells to 1 cell per well into 96-well plates containing a fibroblast feeder layer (BT6) derived from bovine fetal thymus tissue, as described previously (1) .
- In some experiments, sorted cells infected with sporozoites were inoculated back into the donor animals after 48 h of culture in medium containing 2.5% T-cell growth factor derived from concanavalin A-stimulated PBMC as described previously (26) .
- The inocula were administered subcutaneously on the right side of the neck, and animals were monitored daily for rectal temperature and the appearance of parasitized cells, from day 5 until the experiments were terminated.
- The positive and negative cells in each stained population were sorted to Ͼ98% purity on a FACStar Plus cell sorter, and cytospin smears were prepared and stained by immunofluorescence for detection of parasitized cells in the same way as for lymph node puncture biopsy samples.
Reactions of animals inoculated with cloned autologous cell lines.
- Previous studies had shown that inoculation of cattle with 10 5 or more autologous parasitized cells from recently established cell lines resulted in severe, often fatal infections (5) .
- All of the animals were challenged in two groups, along with susceptible controls, with a lethal dose of T. parva sporozoites at 4 and 12 weeks after the initial infection.
- Two of the animals that initially showed no reaction following inoculation with infected B-cell lines (C193 and C672) developed severe infections with prolonged fever and high levels of parasitosis in regional and contralateral lymph nodes.
- Two of the animals exhibited fever for 1 day, and a few parasites were detected in the regional lymph node of only one animal (B312) for 3 days (data not Phenotypes of parasitized cells in animals infected with defined cell populations.
- In the animal infected with whole PBMC, parasitized cells were found within both the CD4 ϩ and CD4 Ϫ populations, although a majority were CD4 ϩ .
DISCUSSION
- Primary infections of cattle with T. parva are characterized by rapid multiplication of parasitized lymphoblasts which become disseminated throughout the lymphoid system and are responsible for much of the pathology associated with infection (16, 23) .
- This suggested either that relatively few B cells became infected in vivo or that B cells and T cells infected with T. parva differ in their capacities to undergo unregulated growth in vivo.
- The difference between the outcome of these infections and the outcome of those in their previous study (5) probably relates to the use of cloned cell lines which had been heavily selected for growth in vitro and had been maintained in culture for a longer period (10 to 16 weeks) to facilitate cloning and phenotyping.
- Two of the four cattle that received parasitized B cell lines showed no clinical or parasitological reaction and were susceptible to subsequent challenge with sporozoites.
- These observations indicate that the difference in outcome of infection in animals inoculated with infected B cells or T cells is related to differences in growth or regulation of the infected cells rather than merely reflecting the numbers of cells in which the parasite had established infection.
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References
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"Pathogenicity of Theileria parva is..." refers methods in this paper
...5% T-cell growth factor derived from concanavalin A-stimulated PBMC as described previously (26)....
[...]
30 citations
"Pathogenicity of Theileria parva is..." refers background in this paper
...This belief is based principally on the observation that in cattle inoculated with allogeneic parasitized cells, doses of 10(8) or more cells are required to achieve consistent establishment of infection in the cells of recipient animals and successful immunization (3)....
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20 citations
"Pathogenicity of Theileria parva is..." refers methods or result in this paper
...Sporozoites were harvested from salivary glands dissected from infected nymphal Rhipicephalus appendiculatus ticks that had been prefed on rabbits for 5 days as described previously (5)....
[...]
...The difference between the outcome of these infections and the outcome of those in our previous study (5) probably relates to the use of cloned cell lines which had been heavily selected for growth in vitro and had been maintained in culture for a longer period (10 to 16 weeks) to facilitate cloning and phenotyping....
[...]
...Previous studies had shown that inoculation of cattle with 10(5) or more autologous parasitized cells from recently established cell lines resulted in severe, often fatal infections (5)....
[...]
...A dose of 10(5) cells was chosen on the basis of a previous study in which cattle inoculated with this dose of uncloned cells developed severe lethal infections (5)....
[...]
7 citations