We have previously shown that an assay based on detection of anti-Salmonella enterica serotype Typhi
antibodies in supernatant of lymphocytes harvested from patients presenting with
typhoid fever (antibody in lymphocyte supernatant [ALS] assay) can identify 100% of patients with blood culture-confirmed
typhoid fever in Bangladesh. In order to define immunodominant
proteins within the S. Typhi membrane preparation used as
antigen in these prior studies and to identify potential
biomarkers unique to S. Typhi bacteremic patients, we probed microarrays containing 2,724 S. Typhi
proteins with ALS collected at the time of clinical presentation from 10 Bangladeshis with acute
typhoid fever. We identified 62 immunoreactive
antigens when evaluating both the
IgG and
IgA responses. Immune responses to 10 of these
antigens discriminated between individuals with acute
typhoid infection and healthy control individuals from areas where
typhoid infection is endemic, as well as Bangladeshi patients presenting with
fever who were subsequently confirmed to have a nontyphoid illness. Using an ALS
enzyme-linked
immunosorbent assay (ELISA) format and purified
antigen, we then confirmed that immune responses against the
antigen with the highest immunoreactivity (
hemolysin E [HlyE]) correctly identified individuals with acute
typhoid or
paratyphoid fever in Dhaka, Bangladesh. These observations suggest that purified
antigens could be used with ALS and corresponding acute-phase activated B lymphocytes in diagnostic platforms to identify acutely infected patients, even in areas where
enteric fever is endemic.