Immunosuppression

Immunosuppression is any reduction in the immune system's capacity to respond, produced deliberately by drugs or acquired through disease, malnutrition, advanced age or cytotoxic chemotherapy. The drug classes act at identifiable points: corticosteroids suppress transcription of inflammatory genes, calcineurin inhibitors such as tacrolimus block the interleukin-2 signal that licenses T-cell proliferation, antimetabolites starve dividing lymphocytes of purines, and biologics remove one cytokine or one cell lineage. It is a graded state rather than a switch.

The consequences appear in the labelling. Tumour necrosis factor inhibitors carry a boxed warning for serious infection and for reactivation of latent tuberculosis. Rituximab depletes CD20-positive B cells for months and blunts responses to vaccines given in that window. Live attenuated vaccines are contraindicated in significant immunosuppression, and long-term transplant regimens raise squamous cell skin cancer incidence well above background.

The tradeoff has one shape: how much infection and malignancy risk buys how much control of rejection or autoimmunity. That is why laboratory monitoring rather than symptom report governs these drugs, and why suppression is layered from several agents at modest exposure rather than one at high exposure.

Two errors recur. The first treats immunocompromised as a single category, grouping a patient on low-dose methotrexate with one two weeks past a stem cell transplant. The second is the marketing inversion, presenting suppression as a deficiency a peptide can correct because it raised a lymphocyte count in culture. Drug-induced suppression resolves when the drug stops, and adding an immune stimulant to a transplant regimen threatens the graft.