Onset and duration of immunity against Babesia canis infection in dogs vaccinated with antigens from culture supernatants.

It has previously been shown that dogs can be vaccinated against heterologous Babesia canis infection using a vaccine containing soluble parasite antigens (SPA) from in vitro cultures of B. canis and B. rossi that are adjuvanted with saponin. In the present study the onset and duration of immunity of vaccinated dogs were studied. Results showed that 3-26 weeks after initial vaccination, dogs effectively limit the level of SPA in plasma upon challenge infection, which was reflected in limited duration and extent of clinical manifestations. There was no statistically significant effect of vaccination on the parasite load in the circulation, which was determined from blood smears. It was further shown that the level of immunity of primary vaccinated dogs (priming and booster vaccination with a 6-week interval) and that of repeatedly vaccinated dogs (a single additional vaccination 6 months after primary vaccination) is comparable. From this study it is concluded that vaccination with this preparation induces protective immunity against clinical babesiosis from 3 weeks after booster vaccination onwards, and remains effective for a period of at least another 6 months. A single booster vaccination is sufficient to maintain immunity for at least another 6 months.

A 31P-NMR study on the recovery of intracellular pH in LLC-PK1/Cl4 cells from intracellular alkalinization.

The regulation of intracellular pH (pHi) in a renal epithelial cell line, LLC-PK1/Cl4, during re-acidification from an alkaline load was studied by 31P-NMR. Intracellular alkalinization was induced by 10 mM ammonium glucuronate or by preloading with and subsequent removal of 20% CO2; the rate of re-acidification was found to be 0.047 pH units/min and 0.053 pH units/min, respectively. This rate of re-acidification was inhibited by 83% if Cl- was removed from the extracellular medium. A similar inhibition was found in the presence of 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS) (76% inhibition) and 1 mM bumetanide (81% inhibition). No change in recovery was found after removing sodium from the extracellular medium, indicating that LLC-PK1/Cl4 cells recover from an intracellular alkaline load by a Cl-/HCO3- exchanger, which is SITS- and bumetanide-sensitive and has no requirement for sodium. In addition, the steady-state pHi in Cl4 cells was monitored by 31P-NMR. Removal of Cl- from the extracellular medium introduced an increase in pHi by 0.33 pH units, whereas 1 mM SITS and 1 mM bumetanide caused an increase in pHi by 0.14 or 0.13 pH units. In the presence of 1 mM amiloride, an inhibitor of the Na+/H+ exchanger, the steady-state pHi did not change significantly. These results indicate that at pHo 7.4 the steady-state intracellular pH of LLC-PK1/Cl4 cells strongly depends on the activity of the Cl-/HCO3- exchanger. Under the same conditions the activity of the Na+/H+ exchanger seems to be negligible.