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infecting these children were relatively conserved among different and subtype families. sequences were relatively conserved among infecting species and subtype families. Although most children were infected with antigen. These results support further development of p23 as a vaccine CLEC4M candidate. Introduction spp. of the phylum Apicomplexa are a significant cause of diarrheal illness worldwide,1,2 particularly in untreated patients with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) and children in resource-poor countries.3C5 In these countries, cryptosporidiosis in early childhood is associated with subsequent malnutrition, impairment in growth, physical fitness, and cognitive development.3,4 The immune system of the host is critical in mediating protection from and resolution of cryptosporidiosis.6 In immunocompetent hosts, the infection is generally asymptomatic or self-limited. However, in immunocompromised hosts including patients with HIV/AIDS, the disease can be chronic, severe, and possibly fatal.7 Therapeutic options for cryptosporidiosis are limited. Nitazoxanide is effective in immunocompetent hosts and is the only drug that has been approved by the Food and Drug Administration for treatment of cryptosporidiosis in the United States.8 However, this drug is not effective in the immunocompromised host9 and has not been widely tested in children in developing countries. Children in these countries are considered an important target group for vaccine development.10 However, there is no vaccine available for cryptosporidiosis. Thus, identification of putative protective antigens and characterization of Tirofiban Hydrochloride Hydrate human immune responses to them is essential for development of effective vaccines for this disease in vulnerable populations. One of these antigens is p23 (also known as Cp23, p27 or 27-kDa antigen), which is a surface-associated, immunodominant antigen present on invasive stages of the parasite and shed from their surface during gliding motility.11C14 Monoclonal and bovine colostral Tirofiban Hydrochloride Hydrate antibodies to p23 protect against challenge in mice and calves, respectively.11,12,15C18 The p23 antigen induces serum, mucosal, humoral, and cell-mediated immune responses in experimentally infected or immunized animals,19C26 and active immunization Tirofiban Hydrochloride Hydrate with DNA or peptide vaccines targeting p23 has been shown to confer varying degrees of protection in animal models.27C29 The p23 antigen is one of the most immunodominant antigens and is consistently recognized by serum from actively infected or Tirofiban Hydrochloride Hydrate previously exposed humans.30C36 The presence of pre-existing antibodies to this antigen was associated with reduced oocyst shedding and protection from diarrhea in infected human volunteers.37 In addition, serum antibody responses to p23 were associated with a reduced risk of diarrheal illness in immunosuppressed persons.38 The p23 antigen also induced cell-mediated and antibody responses in persons previously exposed to spp.39 Taken together, these findings identify p23 as Tirofiban Hydrochloride Hydrate a putative vaccine candidate. This antigen is considered one of the most promising candidates for vaccine development.40 However, there have been few clinical studies of immune responses to this antigen in well-defined cohorts, particularly in children in resource-poor countries. Most infections are caused by two species: almost exclusively infects humans, whereas infects humans in addition to animals.41 Most human infections, particularly in resource-poor countries, are caused by proteins including gp4042,43 and Muc4 and 544 are highly polymorphic among clinical isolates of different species and subtypes. If p23 is to be considered as a vaccine candidate, it is essential to investigate polymorphisms in the gene that encodes it among clinical isolates in different geographic areas. A previous investigation of isolates found ten nucleotide polymorphisms between and three of which result in amino acid changes.45 However, polymorphisms in this gene have not been extensively investigated in samples from clinical studies in different geographic areas. The present study is part of a prospective caseCcontrol study to evaluate the clinical, epidemiologic, and immunologic features of cryptosporidiosis in children with diarrhea coming to the Dhaka Hospital of the International Center for Diarrheal Disease Research (ICDDR, B) in Dhaka, Bangladesh. We previously reported the clinical and epidemiologic features and immune responses.