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Homeostatic proliferation and IL-7R alpha expression do not correlate with enhanced T cell proliferation and protection in chronic mouse malaria.

Stephens R, Seddon B, Langhorne J - PLoS ONE (2011)

Bottom Line: We have previously observed that chronic malaria infection enhances protection to re-infection, as well as enhancing B cell responses.Here, we show that chronic Plasmodium chabaudi malaria infection in mice enhances the expansion of CD4(+) T cells in a second infection, and that this correlates with increased expression of the IL-2/15 Receptor beta (CD122) on memory T cells, as well as increasing IL-2 producers on re-infection.Increased IL-7Rα (CD127) expression correlated, as previously reported with increased turnover of CD4 memory cells, however, this was not linked to protection or enhanced response to rechallenge, These data support the idea that antigen or IL-2 production resulting from chronic stimulation may play a role in an enhanced secondary T cell response.

View Article: PubMed Central - PubMed

Affiliation: Division of Parasitology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom.

ABSTRACT
While chronic infection has been shown to enhance protection from disease caused by several pathogens, the mechanisms are not known. The gamma-c family of cytokines IL-7, IL-2, and IL-15 are implicated in homeostatic proliferation, which is thought to maintain T cell memory. However in chronic infection, prolonged antigen exposure itself may contribute to lymphocyte survival. We have previously observed that chronic malaria infection enhances protection to re-infection, as well as enhancing B cell responses. Here, we show that chronic Plasmodium chabaudi malaria infection in mice enhances the expansion of CD4(+) T cells in a second infection, and that this correlates with increased expression of the IL-2/15 Receptor beta (CD122) on memory T cells, as well as increasing IL-2 producers on re-infection. IL-2 has been recently linked to improved secondary proliferation, while the role of IL-7 in maintenance of CD4(+) memory cells has been demonstrated in homeostatic proliferation, but its role in protective memory populations in infectious disease protective has not been fully investigated. Increased IL-7Rα (CD127) expression correlated, as previously reported with increased turnover of CD4 memory cells, however, this was not linked to protection or enhanced response to rechallenge, These data support the idea that antigen or IL-2 production resulting from chronic stimulation may play a role in an enhanced secondary T cell response.

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Chronic phase of a P. chabaudi infection enhances CD4+ Memory T cell activation and expansion.Mice were infected with 105 P. chabaudi (AS). On days 30-34 one group of mice was treated with chloroquine (+CQ), which quickly eliminated the infection, while the other mice retained a chronic infection (-CQ). A) Half of each group was re-infected with 105 P. chabaudi day 60 post-infection, and splenocytes were analyzed by flow cytometry on day 63 for CD4, CD44, CD62L and expression of the early activation marker CD69 (A–C) or incorporation of BrdU dosed into the water days 60–65 as an indicator of homeostatic proliferation (D, E), CD69 expression on central memory T cells (Tcm, CD44hiCD62lo) and effector memory T cells (Tem, CD44hiCD62Lint/hi) are shown. Dotted lines represent chloroquine treated mice (+CQ) while bold lines represent chronic infection (-CQ). Data shown is the average of 4–5 mice per group and experiment was repeated twice with similar results. * indicates p≤0.05, ** p≤0.01.
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pone-0026686-g001: Chronic phase of a P. chabaudi infection enhances CD4+ Memory T cell activation and expansion.Mice were infected with 105 P. chabaudi (AS). On days 30-34 one group of mice was treated with chloroquine (+CQ), which quickly eliminated the infection, while the other mice retained a chronic infection (-CQ). A) Half of each group was re-infected with 105 P. chabaudi day 60 post-infection, and splenocytes were analyzed by flow cytometry on day 63 for CD4, CD44, CD62L and expression of the early activation marker CD69 (A–C) or incorporation of BrdU dosed into the water days 60–65 as an indicator of homeostatic proliferation (D, E), CD69 expression on central memory T cells (Tcm, CD44hiCD62lo) and effector memory T cells (Tem, CD44hiCD62Lint/hi) are shown. Dotted lines represent chloroquine treated mice (+CQ) while bold lines represent chronic infection (-CQ). Data shown is the average of 4–5 mice per group and experiment was repeated twice with similar results. * indicates p≤0.05, ** p≤0.01.

Mentions: A Plasmodium chabaudi blood-stage infection in C57Bl/6 mice becomes chronic for up to three months [22]. A second infection during the chronic phase leads to a reduced peak parasitemia compared with mice that have either cleared their infection naturally or been treated with anti-malarial drugs [22]. The mechanism of this improved protection is not known. In order to determine whether the extra protection afforded by chronic infection was accompanied by an enhanced CD4+ memory response, we analyzed their activation and proliferation in a second infection, comparing them with CD4+ memory T cells obtained from mice from which the chronic infection had been eliminated (Figure 1). C57Bl/6 mice were infected with 105 P. chabaudi-infected red blood cells and then, after one month, some were treated with the anti-malarial drug, chloroquine (CQ) to cure the infection, preventing the chronic phase. The mice were re-infected, and activation of splenic CD4+ memory T cells by the second infection was measured as an increase in surface expression of the early activation marker CD69, on day 3, when its transient expression can be detected (Figure 1A, B), on both central (Tcm, CD44hiCD62Lhi, Figure 1A, 1B) and effector/effector memory (Tem, CD44hiCD62Llo, Figure 1C) cells. Expression of CD62L was included in this analysis to allow discrimination between proliferation of central memory CD4+ T cells (CD62Lhigh) and effector/effector memory CD4 T cells (CD62Llow). In addition, the proliferation of T cells on re-infection was determined by measuring the incorporation of the thymidine analog, Bromodeoxy Uridine (BrdU) into dividing cells over the first five days of the second infection (Figure 1D, E), when they reach maximal numbers [24] and data not shown). Differences between chronic and treated mice are most clearly seen at day 60 and neither proliferation nor cytokines were detected well at day 3 (data not shown). As well as a significant increase in the proportion of activated Tcm in chronic infection seen in Figure 1B, the number of divided Tcm from mice reinfected during chronic infection (-CQ) was also greater (Figure 1D, E) than that of Tcm from mice treated with Chloroquine (+CQ) after 30 days of infection. While the trend was the same for Tem, only Tcm from chronically infected mice showed significantly enhanced activation. Interestingly, the proportion of CD44hi CD4+ effector and memory T cells is enhanced in chronically infected animals before re-infection (Figure 1F). It is notable that the increases in activation and proliferation measured (using CD69 and BrdU) here reflect the combination of the effects of enhanced specific memory T cell frequency after clonal expansion as well as the enhanced intrinsic responsiveness of individual specific memory T cells to re-infection. There may also be an effect of non-specific stimuli resulting from the continued infection. While there is clearly an advantage to having more memory T cells in malaria [25], we have also shown that similar numbers of MSP1-specific memory cells from chronically infected animals protects RAGo mice better than memory T cells from treated animals [26], suggesting that chronically stimulated memory cells are intrinsically more protective and that multiple effects are involved in the memory T cell response to malaria infection.


Homeostatic proliferation and IL-7R alpha expression do not correlate with enhanced T cell proliferation and protection in chronic mouse malaria.

Stephens R, Seddon B, Langhorne J - PLoS ONE (2011)

Chronic phase of a P. chabaudi infection enhances CD4+ Memory T cell activation and expansion.Mice were infected with 105 P. chabaudi (AS). On days 30-34 one group of mice was treated with chloroquine (+CQ), which quickly eliminated the infection, while the other mice retained a chronic infection (-CQ). A) Half of each group was re-infected with 105 P. chabaudi day 60 post-infection, and splenocytes were analyzed by flow cytometry on day 63 for CD4, CD44, CD62L and expression of the early activation marker CD69 (A–C) or incorporation of BrdU dosed into the water days 60–65 as an indicator of homeostatic proliferation (D, E), CD69 expression on central memory T cells (Tcm, CD44hiCD62lo) and effector memory T cells (Tem, CD44hiCD62Lint/hi) are shown. Dotted lines represent chloroquine treated mice (+CQ) while bold lines represent chronic infection (-CQ). Data shown is the average of 4–5 mice per group and experiment was repeated twice with similar results. * indicates p≤0.05, ** p≤0.01.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3198788&req=5

pone-0026686-g001: Chronic phase of a P. chabaudi infection enhances CD4+ Memory T cell activation and expansion.Mice were infected with 105 P. chabaudi (AS). On days 30-34 one group of mice was treated with chloroquine (+CQ), which quickly eliminated the infection, while the other mice retained a chronic infection (-CQ). A) Half of each group was re-infected with 105 P. chabaudi day 60 post-infection, and splenocytes were analyzed by flow cytometry on day 63 for CD4, CD44, CD62L and expression of the early activation marker CD69 (A–C) or incorporation of BrdU dosed into the water days 60–65 as an indicator of homeostatic proliferation (D, E), CD69 expression on central memory T cells (Tcm, CD44hiCD62lo) and effector memory T cells (Tem, CD44hiCD62Lint/hi) are shown. Dotted lines represent chloroquine treated mice (+CQ) while bold lines represent chronic infection (-CQ). Data shown is the average of 4–5 mice per group and experiment was repeated twice with similar results. * indicates p≤0.05, ** p≤0.01.
Mentions: A Plasmodium chabaudi blood-stage infection in C57Bl/6 mice becomes chronic for up to three months [22]. A second infection during the chronic phase leads to a reduced peak parasitemia compared with mice that have either cleared their infection naturally or been treated with anti-malarial drugs [22]. The mechanism of this improved protection is not known. In order to determine whether the extra protection afforded by chronic infection was accompanied by an enhanced CD4+ memory response, we analyzed their activation and proliferation in a second infection, comparing them with CD4+ memory T cells obtained from mice from which the chronic infection had been eliminated (Figure 1). C57Bl/6 mice were infected with 105 P. chabaudi-infected red blood cells and then, after one month, some were treated with the anti-malarial drug, chloroquine (CQ) to cure the infection, preventing the chronic phase. The mice were re-infected, and activation of splenic CD4+ memory T cells by the second infection was measured as an increase in surface expression of the early activation marker CD69, on day 3, when its transient expression can be detected (Figure 1A, B), on both central (Tcm, CD44hiCD62Lhi, Figure 1A, 1B) and effector/effector memory (Tem, CD44hiCD62Llo, Figure 1C) cells. Expression of CD62L was included in this analysis to allow discrimination between proliferation of central memory CD4+ T cells (CD62Lhigh) and effector/effector memory CD4 T cells (CD62Llow). In addition, the proliferation of T cells on re-infection was determined by measuring the incorporation of the thymidine analog, Bromodeoxy Uridine (BrdU) into dividing cells over the first five days of the second infection (Figure 1D, E), when they reach maximal numbers [24] and data not shown). Differences between chronic and treated mice are most clearly seen at day 60 and neither proliferation nor cytokines were detected well at day 3 (data not shown). As well as a significant increase in the proportion of activated Tcm in chronic infection seen in Figure 1B, the number of divided Tcm from mice reinfected during chronic infection (-CQ) was also greater (Figure 1D, E) than that of Tcm from mice treated with Chloroquine (+CQ) after 30 days of infection. While the trend was the same for Tem, only Tcm from chronically infected mice showed significantly enhanced activation. Interestingly, the proportion of CD44hi CD4+ effector and memory T cells is enhanced in chronically infected animals before re-infection (Figure 1F). It is notable that the increases in activation and proliferation measured (using CD69 and BrdU) here reflect the combination of the effects of enhanced specific memory T cell frequency after clonal expansion as well as the enhanced intrinsic responsiveness of individual specific memory T cells to re-infection. There may also be an effect of non-specific stimuli resulting from the continued infection. While there is clearly an advantage to having more memory T cells in malaria [25], we have also shown that similar numbers of MSP1-specific memory cells from chronically infected animals protects RAGo mice better than memory T cells from treated animals [26], suggesting that chronically stimulated memory cells are intrinsically more protective and that multiple effects are involved in the memory T cell response to malaria infection.

Bottom Line: We have previously observed that chronic malaria infection enhances protection to re-infection, as well as enhancing B cell responses.Here, we show that chronic Plasmodium chabaudi malaria infection in mice enhances the expansion of CD4(+) T cells in a second infection, and that this correlates with increased expression of the IL-2/15 Receptor beta (CD122) on memory T cells, as well as increasing IL-2 producers on re-infection.Increased IL-7Rα (CD127) expression correlated, as previously reported with increased turnover of CD4 memory cells, however, this was not linked to protection or enhanced response to rechallenge, These data support the idea that antigen or IL-2 production resulting from chronic stimulation may play a role in an enhanced secondary T cell response.

View Article: PubMed Central - PubMed

Affiliation: Division of Parasitology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom.

ABSTRACT
While chronic infection has been shown to enhance protection from disease caused by several pathogens, the mechanisms are not known. The gamma-c family of cytokines IL-7, IL-2, and IL-15 are implicated in homeostatic proliferation, which is thought to maintain T cell memory. However in chronic infection, prolonged antigen exposure itself may contribute to lymphocyte survival. We have previously observed that chronic malaria infection enhances protection to re-infection, as well as enhancing B cell responses. Here, we show that chronic Plasmodium chabaudi malaria infection in mice enhances the expansion of CD4(+) T cells in a second infection, and that this correlates with increased expression of the IL-2/15 Receptor beta (CD122) on memory T cells, as well as increasing IL-2 producers on re-infection. IL-2 has been recently linked to improved secondary proliferation, while the role of IL-7 in maintenance of CD4(+) memory cells has been demonstrated in homeostatic proliferation, but its role in protective memory populations in infectious disease protective has not been fully investigated. Increased IL-7Rα (CD127) expression correlated, as previously reported with increased turnover of CD4 memory cells, however, this was not linked to protection or enhanced response to rechallenge, These data support the idea that antigen or IL-2 production resulting from chronic stimulation may play a role in an enhanced secondary T cell response.

Show MeSH
Related in: MedlinePlus