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Kinetics of mosquito-injected Plasmodium sporozoites in mice: fewer sporozoites are injected into sporozoite-immunized mice.

Kebaier C, Voza T, Vanderberg J - PLoS Pathog. (2009)

Bottom Line: Sporozoites injected into immunized mice were rapidly immobilized, did not appear to invade dermal blood vessels and became morphologically degraded within several hours.Strikingly, mosquitoes introduced significantly fewer sporozoites into immunized than into non-immunized mice, presumably by formation of an immune complex between soluble sporozoite antigens in the mosquito saliva and homologous host antibodies at the proboscis tip.These results indicate that protective antibodies directed against sporozoites may function both by reducing the numbers of sporozoites injected into immunized hosts and by inhibiting the movement of injected sporozoites into dermal blood vessels.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Parasitology, New York University School of Medicine, New York, New York, United States of America.

ABSTRACT
Malaria is initiated when the mosquito introduces sporozoites into the skin of a mammalian host. To successfully continue the infection, sporozoites must invade blood vessels in the dermis and be transported to the liver. A significant number of sporozoites, however, may enter lymphatic vessels in the skin or remain in the skin long after the mosquito bite. We have used fluorescence microscopy of Plasmodium berghei sporozoites expressing a fluorescent protein to evaluate the kinetics of sporozoite disappearance from the skin. Sporozoites injected into immunized mice were rapidly immobilized, did not appear to invade dermal blood vessels and became morphologically degraded within several hours. Strikingly, mosquitoes introduced significantly fewer sporozoites into immunized than into non-immunized mice, presumably by formation of an immune complex between soluble sporozoite antigens in the mosquito saliva and homologous host antibodies at the proboscis tip. These results indicate that protective antibodies directed against sporozoites may function both by reducing the numbers of sporozoites injected into immunized hosts and by inhibiting the movement of injected sporozoites into dermal blood vessels.

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Mosquito injection of Plasmodium berghei sporozoites into mouse ear pinna.Scatter plot shows numbers of sporozoites remaining at bite site on ear at various times following injection of sporozoites by mosquitoes feeding on non-immunized (control) mice vs. mice actively immunized against sporozoites. Each point shows number of sporozoites left by a single mosquito. (N = total number of mosquito feedings for each time point.) Horizontal bars show medians. After data were log-transformed (see Materials and Methods), a 3-way analysis of variance (ANOVA) showed that the median for control mice at 2 h was significantly reduced (***P = 0.001) compared with 0-time mean; these reduced numbers stabilized at 3 and 6 h. The median number of sporozoites deposited in actively immunized mice at 0-time was reduced by greater than 45% compared with control mice at 0-time (***P<0.001). Counts of sporozoites injected into immunized mice were unreliable after 2 h due to deterioration and fragmentation of sporozoites.
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ppat-1000399-g001: Mosquito injection of Plasmodium berghei sporozoites into mouse ear pinna.Scatter plot shows numbers of sporozoites remaining at bite site on ear at various times following injection of sporozoites by mosquitoes feeding on non-immunized (control) mice vs. mice actively immunized against sporozoites. Each point shows number of sporozoites left by a single mosquito. (N = total number of mosquito feedings for each time point.) Horizontal bars show medians. After data were log-transformed (see Materials and Methods), a 3-way analysis of variance (ANOVA) showed that the median for control mice at 2 h was significantly reduced (***P = 0.001) compared with 0-time mean; these reduced numbers stabilized at 3 and 6 h. The median number of sporozoites deposited in actively immunized mice at 0-time was reduced by greater than 45% compared with control mice at 0-time (***P<0.001). Counts of sporozoites injected into immunized mice were unreliable after 2 h due to deterioration and fragmentation of sporozoites.

Mentions: A summary of numbers of sporozoites visualized at the bite site on the ear pinna after feedings by individual mosquitoes is presented as a scatter plot in Fig. 1. After mosquitoes fed on non-immunized (control) mice, we found a median of 53.5 sporozoites in biopsy specimens taken from the bite site immediately after feeding. We observed no significant differences in the numbers of these sporozoites compared with numbers found in biopsy specimens taken 1 h post feeding. Indeed, contrary to expectations, the median was greater at 1 h (median = 136); this was due to several high “outliers” observed in this 1 h group, resulting in an upwards skewing of the median. Thus, the variance within each of the groups was too great to permit detection of any significant differences between the medians for 0 vs. 1 h. However, there was a greater than 57% reduction in the number of sporozoites found 2 h post-feeding, compared with 0 h; this was highly significant; P = 0.001. Numbers of sporozoites remaining at the bite site after 2 h appeared to stabilize. In vivo gliding motility of sporozoites was high at 0 and 1 h, with a reduction observed at 2 h; no motility seen at 3 h and beyond. This was observed in mice that had been examined only once at either 1, 2, 3 or 6 h; thus the reduction in sporozoite motility over time was not due to sporozoite damage caused by excessive illumination during fluorescence microscopy.


Kinetics of mosquito-injected Plasmodium sporozoites in mice: fewer sporozoites are injected into sporozoite-immunized mice.

Kebaier C, Voza T, Vanderberg J - PLoS Pathog. (2009)

Mosquito injection of Plasmodium berghei sporozoites into mouse ear pinna.Scatter plot shows numbers of sporozoites remaining at bite site on ear at various times following injection of sporozoites by mosquitoes feeding on non-immunized (control) mice vs. mice actively immunized against sporozoites. Each point shows number of sporozoites left by a single mosquito. (N = total number of mosquito feedings for each time point.) Horizontal bars show medians. After data were log-transformed (see Materials and Methods), a 3-way analysis of variance (ANOVA) showed that the median for control mice at 2 h was significantly reduced (***P = 0.001) compared with 0-time mean; these reduced numbers stabilized at 3 and 6 h. The median number of sporozoites deposited in actively immunized mice at 0-time was reduced by greater than 45% compared with control mice at 0-time (***P<0.001). Counts of sporozoites injected into immunized mice were unreliable after 2 h due to deterioration and fragmentation of sporozoites.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2667259&req=5

ppat-1000399-g001: Mosquito injection of Plasmodium berghei sporozoites into mouse ear pinna.Scatter plot shows numbers of sporozoites remaining at bite site on ear at various times following injection of sporozoites by mosquitoes feeding on non-immunized (control) mice vs. mice actively immunized against sporozoites. Each point shows number of sporozoites left by a single mosquito. (N = total number of mosquito feedings for each time point.) Horizontal bars show medians. After data were log-transformed (see Materials and Methods), a 3-way analysis of variance (ANOVA) showed that the median for control mice at 2 h was significantly reduced (***P = 0.001) compared with 0-time mean; these reduced numbers stabilized at 3 and 6 h. The median number of sporozoites deposited in actively immunized mice at 0-time was reduced by greater than 45% compared with control mice at 0-time (***P<0.001). Counts of sporozoites injected into immunized mice were unreliable after 2 h due to deterioration and fragmentation of sporozoites.
Mentions: A summary of numbers of sporozoites visualized at the bite site on the ear pinna after feedings by individual mosquitoes is presented as a scatter plot in Fig. 1. After mosquitoes fed on non-immunized (control) mice, we found a median of 53.5 sporozoites in biopsy specimens taken from the bite site immediately after feeding. We observed no significant differences in the numbers of these sporozoites compared with numbers found in biopsy specimens taken 1 h post feeding. Indeed, contrary to expectations, the median was greater at 1 h (median = 136); this was due to several high “outliers” observed in this 1 h group, resulting in an upwards skewing of the median. Thus, the variance within each of the groups was too great to permit detection of any significant differences between the medians for 0 vs. 1 h. However, there was a greater than 57% reduction in the number of sporozoites found 2 h post-feeding, compared with 0 h; this was highly significant; P = 0.001. Numbers of sporozoites remaining at the bite site after 2 h appeared to stabilize. In vivo gliding motility of sporozoites was high at 0 and 1 h, with a reduction observed at 2 h; no motility seen at 3 h and beyond. This was observed in mice that had been examined only once at either 1, 2, 3 or 6 h; thus the reduction in sporozoite motility over time was not due to sporozoite damage caused by excessive illumination during fluorescence microscopy.

Bottom Line: Sporozoites injected into immunized mice were rapidly immobilized, did not appear to invade dermal blood vessels and became morphologically degraded within several hours.Strikingly, mosquitoes introduced significantly fewer sporozoites into immunized than into non-immunized mice, presumably by formation of an immune complex between soluble sporozoite antigens in the mosquito saliva and homologous host antibodies at the proboscis tip.These results indicate that protective antibodies directed against sporozoites may function both by reducing the numbers of sporozoites injected into immunized hosts and by inhibiting the movement of injected sporozoites into dermal blood vessels.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Parasitology, New York University School of Medicine, New York, New York, United States of America.

ABSTRACT
Malaria is initiated when the mosquito introduces sporozoites into the skin of a mammalian host. To successfully continue the infection, sporozoites must invade blood vessels in the dermis and be transported to the liver. A significant number of sporozoites, however, may enter lymphatic vessels in the skin or remain in the skin long after the mosquito bite. We have used fluorescence microscopy of Plasmodium berghei sporozoites expressing a fluorescent protein to evaluate the kinetics of sporozoite disappearance from the skin. Sporozoites injected into immunized mice were rapidly immobilized, did not appear to invade dermal blood vessels and became morphologically degraded within several hours. Strikingly, mosquitoes introduced significantly fewer sporozoites into immunized than into non-immunized mice, presumably by formation of an immune complex between soluble sporozoite antigens in the mosquito saliva and homologous host antibodies at the proboscis tip. These results indicate that protective antibodies directed against sporozoites may function both by reducing the numbers of sporozoites injected into immunized hosts and by inhibiting the movement of injected sporozoites into dermal blood vessels.

Show MeSH
Related in: MedlinePlus