Sepsis causes extensive apoptosis of lymphocytes, a pathological condition that is frequently associated with hyperthermia. Heat stress has been implicated to repress the activation of an inflammatory mediator, nuclear factor of kappaB (NF-B), which sensitizes cells to apoptosis mediated by inflammatory cytokine, tumor necrosis factor alpha (TNFa). However, the molecular mechanism of hyperthermia-associated loss of T cells remains unclear. We show that hyperthermia causes rapid translocation of IB kinase (IKK) and the NF-B complexes into the plasma membrane-associated lipid rafts in T cells. Heat stress induces aggregation of Carma1 in lipid rafts, which in turn recruits PKC and Bcl10 to the rafts, causing subsequent membrane translocation of the IKK and NF-B signalosomes. Depletion of Carma1 and inhibition of PKC impair the accumulation of NF-B complexes in lipid rafts. Heat stress prohibits the activity of IKK by sequestrating the IKK and NF-B complexes in lipid rafts and by segregating the chaperone protein Hsp90, an essential cofactor for IKK, from the IKK complex. This process ultimately results in functional deficiency of NF-B and renders T cells resistant to TNFa-induced activation of IKK, thereby contributing to the apoptotic loss of T lymphocytes in sepsis-associated hyperthermia.