DEFECTIVE CD2 T-CELL PATHWAY ACTIVATION IN COMMON VARIABLE IMMUNODEFICIENCY (CVID)

Clonal T cell expansion requires simultaneous activation of the TCR an d secondary signals, e.g. CD2, CD4, CD28. Interference of CD2/CD58 int eraction with MoAbs abrogates the primary immune response and antibody production. Given this functional importance of CD2/CD58 interaction for the generation of specific immune responses, we demonstrate for th e first time a defective CD2 pathway activation in patients with CVID (seven children and four adults). The costimulatory effect of monocyte s upon CD2-triggered proliferation was significantly impaired in CVID patients: 4.080 ct/min versus 20.769 ct/min in controls (P < 0.05). Se cond, IL-1, which is a strong comitogenic factor for activation via CD 2 in normal T cells, showed a defective amplifier function of the CD2 pathway in most patients (median 1.714 ct/min in patients versus 17.52 1 ct/min in controls; P < 0.05). In addition, by using a mitogenic com bination of CD2 plus CD45 MoAb, median proliferation of T cells was se verely depressed in patients: 10.577 ct/min versus 34.685 ct/min in co ntrols (P=0.005). In conclusion, the marked dysfunction seen in respon siveness to phytohaemagglutinin (PHA) (median 24.594 ct/min in patient s ver sus 52.229 ct/min in controls; P < 0.001) and after CD2 triggeri ng, together with the unaffected response to TCR-CD3, suggest that the T cell deficiency in CVID is in part due to deficiencies in the CD2 p athway. Since direct activation of protein kinase C (PKC) by phorbol e ster restores defective T cell responses to normal, our results sugges t that an early signal-transducing defect might exist at a step proxim al to PKC activation in patients with CVID.