The effect of influenza (FLU) infection on heterotypic conjugate formation between antigen-presenting cells and T lymphocytes has been studied with FLU-specific T cell clones and FLU-infected B-lymphoblastoid cells (B-LCL). Conjugate formation between FLU-infected B-LCL (FLU+ B-LCL) and T cells was found to be consistently enhanced in comparison with peptide-sensitized or uninfected B-LCL. Treatment of B-LCL with exogenous neuraminidase (NA-NAse) similarly enhanced conjugate formation indicating that increased conjugate formation may be mediated by the viral neuraminidase. Monoclonal antibody blocking experiments revealed that the contribution by CD2/LFA-3 is increased relative to that of LFA-1/ICAM-1 in conjugates between FLU+ B-LCL or NANAse-treated B-LCL and T cell clones. In contrast, both pathways of adhesion contributed equally to conjugate formation between peptide-sensitized B-LCL or control B-LCL and T cell clones. Thus, FLU infection causes increased conjugate formation between antigen-presenting cells and T cells and skews towards CD2/LFA-3-dependent adhesion, independent of T cell receptor signalling.