Latex Agglutination Enables Functional Assessment of Immune Activity and Differentiation of Therapy-Induced Humoral Responses

Systemic activation of the humoral immune system occurs in malignancies, autoimmune diseases, infections, and pregnancy, yet its quantitative assessment with simple laboratory tools remains challenging. We developed a rapid, low-cost latex agglutination test (LAT) as an antigen-agnostic sensor of systemic humoral activation. The assay measures visual agglutination of uncoated 2-μm latex microspheres by serum antibodies and reports a semi-quantitative titer (highest dilution with visible agglutination). Sera from cancer patients, pregnant women, and healthy volunteers were tested. Uncoated beads revealed increased systemic activity in select groups: in breast cancer (n=11), 73% maintained low titers (≤1:8) while 27% showed therapy-associated rises up to 1:64; HER2-positive cases exhibited transient or sustained elevations during targeted therapy, and CDK4/6 plus endocrine therapy showed delayed increases. Pregnant women displayed high titers (1:32–1:64), and healthy volunteers were negative. These data indicate that LAT captures systemic activation and can distinguish therapy-associated increases, supporting its use as a universal serological marker that complements antigen-specific assays in clinical and research settings.