Immunology
Core concepts
Understand innate versus adaptive immunity, antigen presentation (MHC I to CD8, MHC II to CD4), T-cell subsets (Th1, Th2, Th17, Treg), and B-cell antibody production. Know complement pathways and the clinical meaning of complement levels. In urology, immunology underpins transplant rejection, autoimmune renal disease, and vaccine/prophylaxis decisions. Familiarize yourself with HLA matching, crossmatching, and the types of rejection (hyperacute, acute cellular, antibody-mediated, chronic).
Traps
Questions often conflate MHC classes or test which cytokine drives which response (e.g., IFN-gamma for Th1, IL-4 for Th2). Hyperacute rejection is preformed antibody-mediated and complement-driven-distinguish it from acute cellular rejection. Another trap: assuming immunosuppression eliminates all rejection risk; antibody-mediated rejection can occur despite therapy. Also watch for confusion between direct and indirect allorecognition.
Rule of thumb
Match the rejection timing to mechanism: minutes-to-hours = preformed antibodies (hyperacute); days-to-weeks = cellular; months-to-years = chronic. Match the MHC class to the responding cell: MHC I → CD8 cytotoxic; MHC II → CD4 helper.
Worked example
A kidney recipient develops fever and rising creatinine on postoperative day 5 with a positive donor-specific antibody and C4d deposition on biopsy. This is antibody-mediated rejection, not simple acute cellular rejection; treatment targets antibodies (plasmapheresis, IVIG) rather than steroids alone.