Heritability estimates of the 54 analyzed ITs was equal to 0.45 on average (se = 0.20; Table 1 For the large set of adaptive ITs, the mean heritability was 0.48 (se = 0.21). No significant difference in average heritability values was detected either between group of ITs qualifying the innate and adaptive immunity or the humoral and cellular adaptive immunity. In addition, an equivalent proportion of innate and adaptive ITs had significant heritability values. Indeed, 40% (10/25), 40% (2/5) and Among the traits involved in cell-mediated immunity, variation in ab T lymphocyte (CD4 -CD8 + , CD4 + CD8 + and CD4 + CD8cells) counts was highly heritable. Heritability estimates of the three cytokine (IL4, IL10, IFNG) levels were moderate to high after PMAIONO and CONA stimulations and weak to moderate after LPS stimulation. For those cytokines induced by CONA or LPS stimulation, confidence interval (95CI) for the heritabilities overlapped zero, except for IL4-CONA. IL2 production after PMAIONO, CONA and LPS stimulations gave high estimates of heritability significantly different from zero for IL2-PMAIONO and IL2-LPS. Proliferation measurements after various stimulations (PROLIF-CONA, PROLIF-PMAIONO, PROLIF-LPS) provided moderate estimates of heritability not significantly different from zero. Among the traits involved in humoralmediated adaptive immunity, heritabilities for total IgG and IgA antibody levels were higher than for total IgM and specific antibodies, and weak h 2 values were obtained for B lymphocyte count (IgM + cells).