Prabhakaran, V (2008) Taenia Solium Metacestode Glycoproteins Diagnostic for Solitary Cysticercus Granuloma. Doctoral thesis, The Tamilnadu Dr. M.G.R. Medical University, Chennai.
Full text not available from this repository.Abstract
In 2003 the World Health Organization recognized that T solium infections were of public health magnitude. This recognition was possible because of improved methods of detection especially by neuro-imaging and serological tests and increased clinical and public awareness of T solium infections. Epidemiological studies during the last twenty years point to a near global prevalence of T solium. There are populations in endemic countries where almost one a quarter of the population is infected with the parasite (225, 226, 227). The seriousness of a CNS infection that causes seizures, raised intracranial pressure, arachnoiditis, hydrocephalus, visual loss, stroke, dementia and can be fatal and which affects a large number of people who do not have access to appropriate health care cannot be over emphasized. The enormity of the problem can be assessed in recognizing that NCC is the most common parasitic infection of the CNS and cause of recent onset seizures in most countries endemic for the infection (225). In India, where epilepsy affects 5 million people, a third is due to NCC in people between the ages of 2 and 60 years (63). The proglottids of T solium with a content of 50-60 thousand eggs are the source of NCC infection. This immense number and density of eggs lends credibility to multi-cyst NCC as the predominant infection in most countries world-wide. It is difficult to comprehend how this quantity of infective eggs gives rise to a solitary cyst infection in the brain in over 66% of patients in the large and dense population of India. The studies of this thesis were an attempt to understand this paradox. Solitary cysticercus granuloma as an infection of T solium and not of M tuberculosis /other infections or a metastatic lesion was first reported in India in 1985 (228). Subsequently increased clinical awareness and improved radiological facilities in the country rapidly established solitary cysticercus granoloma as the predominant form of T solium infection in India. By 1997 radiological images for SCG were well described and images of T solium lesions identified with a sensitivity of 99% (12). However NCC diagnosed by radiology can only be confirmed at follow up. Serological tests confirm diagnosis at initial presentation. They are also not as expensive as radiological imaging and are more available. Although specific and sensitive serological tests were available for multi-cyst NCC from 1989 they had not been tested for solitary cysticercus granuloma infections. Most of these sero-immunoassays utilized T solium cyst glycoproteins as antigens for detection of cysticercus antibodies in infected fluid. Several of these glycoproteins were identified as specific for the parasite with affinity for the lectin from Lens culinaris. These assays exhibited 100% specificity for T solium infections of the CNS (114, 115). In the mid 1990s when solitary cyst infections were realized to predominate in India the available serological tests were found to be inadequate for diagnosis. In one series, cysticercus antibodies were detected in only 28% of patients with a solitary cyst. A low sensitivity of an immune-assay, that utilizes parasite specific antigens to detect antibodies in disease, signifies the production of a small amount of antibodies or the inability of the antibodies to recognize epitopes on the antigens. The poor sensitivity of the immuneassays in detecting cysticercus antibodies in patients with SCG was taken to indicate a condition of low antibody levels produced in response to a low amount of immune suppressive antigens. A sensitive sero-immunological test was therefore considered a primary requirement in this study of NCC in India (166, 211). It is critical that immune-diagnostic tests are specific for an infectious disease in regions of high prevalence. LLGP were considered in antibody detection tests for SCG in view of the excellent specificity they offered in immunoassays for multi-cyst infections. These glycoproteins, extracted from locally acquired cysts in a non-chaotropic medium and purified, were found on immune-blots to detect cysticercus antibodies in 62 % of SCG patients. A sample was considered positive for NCC if antibodies to one or more of the seven glycoproteins 50, 42-38, 24, 21, 18, 14, 13 kDa were present. The tests performed no better than earlier, although mild procedures were employed to extract the proteins from locally acquired cysts, in an attempt to maintain the structure of the antigens. However immunoblots converted to dot blot formats and using each of 6 pure antigens individually provided an immune-assay 50% more sensitive than the original immune blot, in detecting cysticercus antibodies in patients with SCG. The dot blot was not only sensitive but easy to read and interpret and therefore useful in both clinical diagnostics and epidemiology. A further approach taken to improve detection of cysticercus antibodies in SCG infections was to increase the number / affinity of epitopes available on the antigens for antibody binding. Altering the conformation of a protein is well known to change epitope availability and recognition. This approach necessitated structural characterization of the antigens to determine features of the proteins required for antibody recognition. Among six pure antigens most frequently detected by cysticercus antibodies in sera of Indian patients with NCC, N-glycosylation and disulfide links were essential for antibody recognition. Optimal cysticercus antibody binding was noted to ureainduced tertiary conformations of all these proteins. Deglycosylation, unfolding transitions and electrophoretic migration patterns indicated five of the antigenic proteins between 38 and 13 kDa may belong to the 8 kDa protein family. This might explain why all of them exhibited maximal antibody binding in the same conformational state. Conformation-sensitive immunoblots with the cyst glycoproteins in tertiary conformation improved the sensitivity of detecting cysticercus antibodies in the blood of SCG patients. Almost 50% of sera considered negative for cysticercus antibodies on immune blots using the antigens in quaternary conformation were in fact positive for these antibodies which recognized the tertiary conformation of the proteins. All systems were sensitive in ELISA formats as well. The distinct advantage of the immune blots over ELISA was the ability to determine the specificity of each sample. Sensitive and specific sero-immunoassays for NCC infections seen in India provided the necessary tool for population based epidemiological studies. The seroprevalence of cysticercus antibodies of 15.9% in a district of Tamilnadu is among the first studies to show the high levels of T solium infection in the general population of Southern India. Prevalence levels of this magnitude classify the region as hyperendemic for T solium infection. A third of all households in the District were found to carry infection which reiterates the magnitude of exposure. The significantly higher levels of infection in the rural population compared to the urban population, who also eat more pork than their urban counter-parts, begs the question as to the mode of transmission of the infection. Determining the risk of occupation (pig rearing) and importance of human to human egg transmission as well as the burden of taeniasis would help towards eradication strategies. Chronic exposure to T solium that occurs in a high prevalence population, as in South India, would influence immunity to T solium infection in an uninfected individual. Chronic intestinal protozoal and helminth infections that occur in 97.4% of the South Indian population would also govern the immune response to T solium infections in these individuals (229). High levels of T solium in the environment, as indicated by the high seroprevalence of infection in the South Indian population and the high egg content of proglottids, suggest Indians are likely to be infected with large numbers of T solium eggs. Predominant solitary cyst infections suggest efficient host inflammatory reactions early in parasite infection that eliminate all or most of the eggs. A multi-cyst infection may arise from an inflammatory response that is unable to eliminate several infecting eggs. Pro-inflammatory immune reactions to Taenia antigens in the periphery in non-infected individuals and anti-inflammatory reactions in both solitary and multi-cyst infections suggest mechanisms of parasite elimination and survival respectively. The reactions are almost completely controlled by the N-glycans of the parasite antigens. Although mixed Th1/Th2 responses occur in infection, a large inflammatory response retained in multi-cyst infections suggests continued host requirement to eliminate the parasite. Pro-inflammatory immune response early in infection protects the host against invasive oncospheres. Elimination of the cyst in anti-inflammatory environments may be through phagocytosis and toxicity from elevated nitric oxide levels. The study signifies the need to understand which molecules of the parasite direct transmission of the host from an early Th1 response to Th2 response and the specific host machinery involved in this temporal shift. This would aid in explaining the peculiarity of low cyst number NCC in India. CONCLUSIONS: It was found on purification and structural characterization of 6 T solium metacestode specific glycoproteins with affinity for Lens culinaris that N-glycosylation and disulfide bonds of the proteins were essential for cysticercus antibody binding and the tertiary conformations of the proteins were optimal for antibody recognition. These properties of the antigenic cyst proteins enabled: 1. Serodiagnosis, in immunoblot format, suitable for detecting cysticercus antibodies in Indian patients with solitary cysticercus granuloma to be established. 2. The seroprevalence of cysticercosis in the general Indian population to be determined as 15.9%. 3. An understanding that immunity in the Indian patient with NCC may transit from early pro-inflammatory reactions that eliminate invasive oncospheres to anti-inflammatory responses that permit parasite to survive in the host. Strong inflammatory immune reactions may eliminate most of the large numbers of invasive oncospheres in T solium infections. A solitary cysticercus granuloma may arise from among a few ova that are not eliminated in these early reactions.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Uncontrolled Keywords: | Neurocysticercosis, Solitary cysticercus granuloma, Taenia solium glycoproteins, India. |
| Subjects: | MEDICAL > Neurology |
| Depositing User: | Subramani R |
| Date Deposited: | 18 Jan 2022 12:45 |
| Last Modified: | 18 Jan 2022 12:45 |
| URI: | http://repository-tnmgrmu.ac.in/id/eprint/19017 |
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