Urinary tract infections (UTIs) are caused by the invasion of microorganisms into the urinary tract, which can include the kidneys, bladder, and urethra. There are three ways in which UTIs can be acquired, and the first one is ascending infection. The latter is the most common route of infection, where bacteria from the rectal or genital area travel up the urethra and into the bladder (Sullivan & Ulett, 2020). The second one is hematogenous spread, where bacteria enter the bloodstream from another site of infection and spread to the urinary tract (Sullivan & Ulett, 2020). The third one is a direct extension, where the infection spreads directly from adjacent structures, such as the prostate gland.
When the body encounters an immunogenic response, the immune system produces two types of antibodies, such as primary and secondary responses. The primary response occurs when the body first encounters the antigen, which is the foreign substance that triggers the immune response. During the primary response, B cells produce IgM antibodies, which are the first line of defense against the antigen (Nivarthi et al., 2019). The secondary response occurs when the body encounters the same antigen a second time. During the secondary response, B cells produce IgG antibodies, which are more specific and have a higher affinity for the antigen.
Acute and convalescent serum specimens are important for the serologic diagnosis of infection. The acute serum is collected during the acute phase of the infection, while convalescent serum is collected 2-4 weeks later (Nivarthi et al., 2019). By comparing the two serum specimens, serologic testing can determine whether the patient has produced a primary or secondary antibody response. A significant increase in IgG antibody levels between the acute and convalescent specimens suggests a secondary response and indicates that the patient has been infected in the past. A single high level of IgM antibodies in the acute serum specimen indicates a primary response and suggests that the patient is currently infected.
References
Nivarthi, U. K., Tu, H. A., Delacruz, M. J., Swanstrom, J., Patel, B., Durbin, A. P., Whitehead, S. S., Pierce, K. K., Kirkpatrick, B. D., Baric, R. S., Nguyen, N., Emerling, D. E., de Silva, A. M., & Diehl, S. A (2019). Longitudinal analysis of acute and convalescent B cell responses in a human primary dengue serotype 2 infection model. eBioMedicine, 41, 465-478. Web.
Sullivan, M. J., & Ulett, G. C. (2020). Evaluation of hematogenous spread and ascending infection in the pathogenesis of acute pyelonephritis due to group B streptococcus in mice. Microbial Pathogenesis, 138, 103796. Web.