Limits...
Prolonged antigen presentation is required for optimal CD8+ T cell responses against malaria liver stage parasites.

Cockburn IA, Chen YC, Overstreet MG, Lees JR, van Rooijen N, Farber DL, Zavala F - PLoS Pathog. (2010)

Bottom Line: Firstly, reducing the time primed CD8+ T cells were exposed to antigen in vivo severely reduced the final size of the developing memory population.Secondly, fully developed memory cells expanded in previously immunized mice but not when transferred to naïve animals.Finally, persisting antigen was able to prime naïve cells, including recent thymic emigrants, to become functional effector cells capable of eliminating parasites in the liver.

View Article: PubMed Central - PubMed

Affiliation: Johns Hopkins Malaria Research Institute and Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Baltimore, Maryland, USA.

ABSTRACT
Immunization with irradiated sporozoites is currently the most effective vaccination strategy against liver stages of malaria parasites, yet the mechanisms underpinning the success of this approach are unknown. Here we show that the complete development of protective CD8+ T cell responses requires prolonged antigen presentation. Using TCR transgenic cells specific for the malaria circumsporozoite protein, a leading vaccine candidate, we found that sporozoite antigen persists for over 8 weeks after immunization--a remarkable finding since irradiated sporozoites are incapable of replication and do not differentiate beyond early liver stages. Persisting antigen was detected in lymphoid organs and depends on the presence of CD11c+ cells. Prolonged antigen presentation enhanced the magnitude of the CD8+ T cell response in a number of ways. Firstly, reducing the time primed CD8+ T cells were exposed to antigen in vivo severely reduced the final size of the developing memory population. Secondly, fully developed memory cells expanded in previously immunized mice but not when transferred to naïve animals. Finally, persisting antigen was able to prime naïve cells, including recent thymic emigrants, to become functional effector cells capable of eliminating parasites in the liver. Together these data show that the optimal development of protective CD8+ T cell immunity against malaria liver stages is dependent upon the prolonged presentation of sporozoite-derived antigen.

Show MeSH

Related in: MedlinePlus

Prolonged antigen presentation after sporozoite immunization.2×106 Thy1.1+ CD8+ T cells from either TCR transgenic or WT animals were transferred into groups of naïve mice or mice immunized 2 weeks previously with 5×104 irradiated P. yoelii sporozoites. 10 days after cell transfer the spleen cells from the recipient mice were analyzed by FACs. Histograms show CFSE profiles of the Thy1.1+ CD8+ cell populations in each group. Values are the mean ± SE of the percentage of divided cells (n = 3, data from one of two similar experiments shown).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2865532&req=5

ppat-1000877-g001: Prolonged antigen presentation after sporozoite immunization.2×106 Thy1.1+ CD8+ T cells from either TCR transgenic or WT animals were transferred into groups of naïve mice or mice immunized 2 weeks previously with 5×104 irradiated P. yoelii sporozoites. 10 days after cell transfer the spleen cells from the recipient mice were analyzed by FACs. Histograms show CFSE profiles of the Thy1.1+ CD8+ cell populations in each group. Values are the mean ± SE of the percentage of divided cells (n = 3, data from one of two similar experiments shown).

Mentions: To determine whether antigen persists following irradiated sporozoite immunization we transferred high numbers of CFSE labeled TCR transgenic Thy1.1+ CD8+ T cells specific for the CS protein of P. yoelii (hereafter referred to as “transgenic cells”) into mice that had been immunized 14 days previously with irradiated P. yoelii sporozoites or naïve control animals. We found that transgenic cells in previously immunized mice, but not naïve controls, had some dilution of the CFSE label showing that some of the cells had proliferated (Figure 1). T cell proliferation was not seen among polyclonal T cells from WT Thy1.1+ mice transferred to immune mice, indicating that proliferation was antigen specific and not due to bystander activation (Figure 1). Moreover, immunization with the related parasite P. berghei which express a different CD8+ epitope not recognized by our transgenic cells also failed to induce specific T cell proliferation further excluding the possibility of bystander activation (Figure S1A).


Prolonged antigen presentation is required for optimal CD8+ T cell responses against malaria liver stage parasites.

Cockburn IA, Chen YC, Overstreet MG, Lees JR, van Rooijen N, Farber DL, Zavala F - PLoS Pathog. (2010)

Prolonged antigen presentation after sporozoite immunization.2×106 Thy1.1+ CD8+ T cells from either TCR transgenic or WT animals were transferred into groups of naïve mice or mice immunized 2 weeks previously with 5×104 irradiated P. yoelii sporozoites. 10 days after cell transfer the spleen cells from the recipient mice were analyzed by FACs. Histograms show CFSE profiles of the Thy1.1+ CD8+ cell populations in each group. Values are the mean ± SE of the percentage of divided cells (n = 3, data from one of two similar experiments shown).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2865532&req=5

ppat-1000877-g001: Prolonged antigen presentation after sporozoite immunization.2×106 Thy1.1+ CD8+ T cells from either TCR transgenic or WT animals were transferred into groups of naïve mice or mice immunized 2 weeks previously with 5×104 irradiated P. yoelii sporozoites. 10 days after cell transfer the spleen cells from the recipient mice were analyzed by FACs. Histograms show CFSE profiles of the Thy1.1+ CD8+ cell populations in each group. Values are the mean ± SE of the percentage of divided cells (n = 3, data from one of two similar experiments shown).
Mentions: To determine whether antigen persists following irradiated sporozoite immunization we transferred high numbers of CFSE labeled TCR transgenic Thy1.1+ CD8+ T cells specific for the CS protein of P. yoelii (hereafter referred to as “transgenic cells”) into mice that had been immunized 14 days previously with irradiated P. yoelii sporozoites or naïve control animals. We found that transgenic cells in previously immunized mice, but not naïve controls, had some dilution of the CFSE label showing that some of the cells had proliferated (Figure 1). T cell proliferation was not seen among polyclonal T cells from WT Thy1.1+ mice transferred to immune mice, indicating that proliferation was antigen specific and not due to bystander activation (Figure 1). Moreover, immunization with the related parasite P. berghei which express a different CD8+ epitope not recognized by our transgenic cells also failed to induce specific T cell proliferation further excluding the possibility of bystander activation (Figure S1A).

Bottom Line: Firstly, reducing the time primed CD8+ T cells were exposed to antigen in vivo severely reduced the final size of the developing memory population.Secondly, fully developed memory cells expanded in previously immunized mice but not when transferred to naïve animals.Finally, persisting antigen was able to prime naïve cells, including recent thymic emigrants, to become functional effector cells capable of eliminating parasites in the liver.

View Article: PubMed Central - PubMed

Affiliation: Johns Hopkins Malaria Research Institute and Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Baltimore, Maryland, USA.

ABSTRACT
Immunization with irradiated sporozoites is currently the most effective vaccination strategy against liver stages of malaria parasites, yet the mechanisms underpinning the success of this approach are unknown. Here we show that the complete development of protective CD8+ T cell responses requires prolonged antigen presentation. Using TCR transgenic cells specific for the malaria circumsporozoite protein, a leading vaccine candidate, we found that sporozoite antigen persists for over 8 weeks after immunization--a remarkable finding since irradiated sporozoites are incapable of replication and do not differentiate beyond early liver stages. Persisting antigen was detected in lymphoid organs and depends on the presence of CD11c+ cells. Prolonged antigen presentation enhanced the magnitude of the CD8+ T cell response in a number of ways. Firstly, reducing the time primed CD8+ T cells were exposed to antigen in vivo severely reduced the final size of the developing memory population. Secondly, fully developed memory cells expanded in previously immunized mice but not when transferred to naïve animals. Finally, persisting antigen was able to prime naïve cells, including recent thymic emigrants, to become functional effector cells capable of eliminating parasites in the liver. Together these data show that the optimal development of protective CD8+ T cell immunity against malaria liver stages is dependent upon the prolonged presentation of sporozoite-derived antigen.

Show MeSH
Related in: MedlinePlus