In vivo killing of Giardia trophozoites harbouring bacterial endosymbionts by intestinal Paneth cells: an ultrastructural study
To date Paneth cells have not previously been reported to kill Giardia trophozoites and other protozoa in vivo. Here we report the first evidence for in vivo killing of Giardia trophozoites by intestinal Paneth cells. Transmission electron microscopic (TEM) examination of duodenal specimens taken from naturally infected mice revealed that only Giardia trophozoites harbouring peripheral bacterial endosymbionts were destroyed and lysed in the vicinity of the activated Paneth cells. Additionally, intestinal epithelium was more affected by Giardia harbouring bacterial endosymbionts than Giardia with no endosymbionts. Our findings imply that the bacterial endosymbionts within Giardia trophozoites have a role in both host protective and pathological mechanisms, probably through altering the trophozoite antigencity. These observations might shed light on the diversity in infectivity and host specificity of Giardia species.(Received January 1 2004)
(Revised August 10 2004)
(Accepted August 10 2004)
Key Words: endosymbiosis; giardiasis; electron microscopy; Paneth cells; in vivo killing; naturally infected mice.
c1 Microbiology Department, College of Medicine and Medical Sciences, King Khalid University, P.O. Box 641, Abha, Kingdom of Saudi Arabia. Fax: 00966 72247570. E-mail: Khel666@hotmail.com