Potential mechanisms of poor CD41 T cell reconstitution after viral suppression with antiretroviral therapy (ART) in HIV disease have been extensively investigated. We recently discovered that anti-CD4 autoantibody plays a role in impaired CD41 T cell recovery from ART in HIV-infected individuals with viral suppression, which accounts for a mechanism specific for CD41 T cell depletion. However, the mechanism of pathological anti-CD4 autoantibody production in treated HIV disease remains unknown. Here, we report that seasonal influenza vaccination induced IgG anti-CD4 autoantibodies, predominantly of the IgG3 subclass, in some virus-suppressed ART-treated HIV1 subjects. To explore the mechanism of anti-CD4 antibody production in this population, we performed and analyzed gene profiles in isolated B cells using a gene microarray and 32 plasma cytokines. Notably, both gene expression and multiple cytokine analyses showed that interleukin 23 (IL-23), at the prevaccination plasma level, was the key cytokine linked to IgG anti-CD4 antibody production in response to immunization in vivo. Exogenous recombinant IL-23 (rIL-23) increased autoreactive IgG binding on CD41 T cells from HIV1 subjects in vitro. Results from this study may reveal a role of IL-23 in anti-CD4 autoantibody production in treated HIV. IMPORTANCE In our published studies (Z. Luo et al., J Leukoc Biol 102:1481–1486, 2017, https://doi.org/10.1189/jlb.5A0617-219R; Z. Luo et al., J Infect Dis 216:82–91, 2017, https://doi.org/10.1093/infdis/jix223), we determined that pathological anti-CD4 IgGs from immunologic nonresponders on virally suppressive ART (CD4 cell counts, 350 cells/ml) mediated CD41 T cell death via antibody-mediated cytotoxicity (ADCC), which plays a role in poor CD41 T cell recovery from ART. Up to 25% of HIV-infected individuals are nonresponders and demonstrate increased morbidity and mortality. However, the mechanism of anti-CD4 autoantibody production in treated HIV remains unknown. In this study, we report that IL-23 may be the key cytokine to promote anti-CD4 autoantibody production after immunization in ART-treated HIV-infected individuals.