Profiling the cellular immune response to multiple Brugia pahangi infections in a susceptible host

Human lymphatic filariasis is caused primarily by Brugia malayi and Wuchereria bancroffi. Unraveling this disease is complex, as people living in endemic areas exhibit a vast array of clinical states and immune responses. The Mongolian gerbil (Meriones unguiculatus)-B. pahangi model of human lymphatic filariasis has provided much information on immune parameters associated with filarial infection. Prior investigations in our laboratory have shown that gerbils closely mimic a subset of patients classified as microfilaremic but asymptomatic, a group that comprises the majority of people living in endemic areas. Worm recovery data suggest that gerbils carrying current B. pahangi infections do not show any resistance to subsequent subcutaneous B. pahangi infections. The aim of the present studies was to investigate the T cell cytokine response in gerbils receiving multiple infections of B. pahangi as a means of mimicking the conditions experienced by people in endemic areas. The T cell cytokine profile generated by multiply infected gerbils was not different from that previously generated by gerbils infected only once with B. pahangi. Gerbils infected multiple times with B. pahangi showed a transient increase in IL-5, which corresponded to the increased eosinophil levels previously reported from multiply infected gerbils. Chronically infected gerbils showed elevated IL-4 mRNA levels, as has been reported from gerbils infected only once with B. pahangi. Chronic infections were also associated with a state of immune hyporesponsiveness, as determined by the characterization of lymphatic thrombi and lymphoproliferation of spleen and renal lymph node cells to worm antigen.

Kinetics of T cell cytokine gene expression in gerbils after a primary subcutaneous Brugia pahangi infection

The majority of patients infected with lymphatic filariae are microfilaremic but tend to manifest little obvious pathology because of the infections. Data collected from the Mongolian gerbil-Brugia spp. model for human lymphatic filariasis suggest this experimental animal model system most closely represents this patient group and will be useful in studying immunological parameters associated with chronic infections. This article reports the quantitation of interleukin (IL)-4, IL-5, IL-10, IL-13, and interferon (IFN)-gamma messenger RNA (mRNA) in gerbils after a primary subcutaneous infection with Brugia pahangi. Chronically infected gerbils showed elevated IL-4 in all tissues, compared with earlier time points, linking this Th2 cytokine to the downregulation of responsiveness, which develops in gerbils and humans. Both IL-5 and IL-13 mRNA expression were transient in all tissues. The peak in IL-5 at 14-28 days postinfection reflects the peak of peripheral eosinophilia observed in B. pahangi-infected gerbils. Little IFN-gamma mRNA was reported from chronically infected gerbils. The data collected thus far suggest that the expression profile of many of the measured cytokines in B. pahangi-infected gerbils reflects what is seen in an important subset of humans infected with lymphatic filariae, the microfilaremic, asymptomatic patient.

Exsheathment of Ostertagia ostertagi infective larvae following exposure to bovine rumen contents derived from low and high roughage diets

The objective of this study was to characterize the exsheathment kinetics of Ostertagia ostertagi infective larvae (L3) following in vivo exposure to bovine rumen contents derived from low and high roughage diets. O. ostertagi L3 were placed in disposable dialysis bags and incubated for various time points between 0 and 360 min in the rumen of a fistulated steer maintained on a 71% grain diet or a 100% grass diet. The maximum percentage of exsheathed L3 was observed 120 min post-exposure to grass-derived rumen contents, while maximum exsheathment for L3 exposed to grain-derived rumen contents did not occur until 360 min. This work provides the first report of the in vivo exsheathment kinetics for O. ostertagi in its bovine host. Results of this study also support earlier reports that rumen pH may affect the exsheathment efficiency of abomasal trichostrongylids.

The filarial endosymbiont Wolbachia sp. is absent from Setaria equina

Wolbachia sp. was first reported in filarial nematodes over 25 yr ago. Today, much research is focused on the role of these bacteria in filarial worm biology. The filarial symbionts are closely related to arthropod symbionts, which are known to modify host reproduction and biology through various mechanisms. Similarly, it has been suggested that Wolbachia sp. is essential for long-term survival and reproduction of filariae. We report that Wolbachia sp. 16S rDNA was not found in the equine filarial nematode Setaria equina, using either polymerase chain reaction (PCR) or DNA hybridization. In addition, ultrastructural analysis of adult worms did not reveal the presence of Wolbachia sp. in hypodermal cords or reproductive tissues. These data suggest that like Onchocerca flexuosa and Acanthocheilonema vitae, S. equina may not be dependent on Wolbachia sp. for survival.