Inter and intra-specific developmentally regulated antigenic polymorphisms and some metabolic differences between promastigotes of Leishmania donovani and L. major have been characterized. There was an increase in optical density values from logarithmic to stationary phase antigen of both species justifying the increased infectivity of stationary phase promastigotes. Immunoblot analysis showed few antigens as species and stage-specific, viz., 105 KDa unique to L. donovani logarithmic phase, 140 KDa to logarithmic phase of L. major and 115 KDa to L. major stationary phase promastigotes, whereas antigen of 50 KDa was only present in logarithmic phase of both L. donovani and L. major strain. Bands at 20, 95 and 120 KDa were present both in logarithmic and stationary phase L. donovani antigen when they reacted with homologous antibody. On the other hand, no common shared antigens were detected in the case of homologous reaction of two phases of L. major strain. Fewer peptides on western blots of stationary phase than of logarithmic phase promastigotes confirmed the concept that the former phase may be less immunogenic but much more infective to its vertebrate host. Of the amino acids and sugars tested, proline was found to have the maximum role in the transformation to metacyclic form. The role of the other sugars were negligible.
Cross reactivity of Babesia rodhaini (B. rodhaini) and Babesia microti (B. microti) antigens against Babesia-chronically infected mice sera was examined using indirect fluorescent antibody (IFA) technique and westernblotting. The effect of monoclonal antibody #7 (mAb #7), which recognized both B. microti and B. rodhaini antigens, was also studied against Babesia-infections. Passive immunization with mAb #7 was carried out to clarify the relationship between cross-reactive antigens and progression of Babesia infection. Results of IFA assay showed cross reactivity in B. microti and B. rodhaini antisera at a dilutions of 1:512 and 1:128, respectively. Each type of antiserum exhibited parasite specific fluorescence. Immunoblotting demonstrated the reactivity of B. microti and B. rodhaini antisera with the 70 and 32 kilodaltons (kDa) B. rodhaini antigens, and with the 70 kDa B. microti antigen, respectively. These results suggest a stronger cross reactivity of B. microti antiserum compared to B. rodhaini antiserum. Monoclonal antibody #7 reacted with 70 and 30 kDa antigens of B. microti, and with 70 and 32 kDa antigens of B. rodhaini. Passive immunization using mAb #7 showed a delayed development in high levels of parasitemia in both Babesia spp., compared to the control groups. These results demonstrate the apparent role of mAb #7 in suppressing the onset of parasitemia.
The precise reason for variability of disease spectrum in Giardia lamblia infested persons is not understood, but host immunity (especially local immunity) appears to be an important contributory factor. To study the interaction between host and the parasite in the small intestine, it is important to study the local cell mediated immune response to understand the pathophysiology of giardiasis. For this, in the present study the T-lymphocyte subsets were studied in intestines of BALB/c mice infected with different G. lamblia strains isolated from asymptomatic and symptomatic patients. An increase in percentages of CD3+ cells (Thy 1+) and B cells was observed, with a peak on 12th day post inoculation. There was also an increase in CD4+ cells (L3T4+) which reached a peak on 12th and 18th day post inoculation in mice infected with strains isolated from asymptomatic and symptomatic patients respectively. CD8+ (Lyt2+) cells were also slightly elevated and peaked at 12th and 24th day post inoculation in mice infected with asymptomatic and symptomatic strains respectively. It is therefore suggested that the increase in CD4+ cells may be beneficial to the host as it correlated directly with the elimination of the parasite and thus these cells might play an important role in pathogenesis of diarrhoea caused by this parasite.
Basic method for in vitro cultivation of Babesia ovata was examined using a method which was developed by Vega et al. for cultivation of B. bigemina, a closely related organism. The parasites obtained from an infected SCID mouse were initiated their multiplication within adult bovine RBC in Medium 199 supplemented with 40% adult bovine serum under a low oxygen atmosphere, 5% O2, 5% CO2 and 90% N2. Although no proliferation of B. ovata maintained in 5% CO2 in air was seen during the initial 5 days, the parasites passaged three times under the low oxygen atmosphere were readily cultured in 5% CO2 in air, as well as under the low oxygen atmosphere. The parasites were propagated in the RBC stored in Vega y Martinez solution at 4℃ for up to 2 months. Babesia ovata-infected RBC from cultures were successfully cryopreserved in 10% polyvinylpyrrolidone in Vega y Martinez solution and used to initiate new culture not only under the low oxygen atmosphere but also in 5% CO2 in air.