<prompt> Helper cells belong to -T cellsMacrophagesB cellsMonocytes  <response>: Ans. is a i..e.,T cells T-cells . T cells are amongst the two impoant cells of adaptive immune system others are B-cells. . T cell precursors arise in bone marrow also in yolk sac liver before bih and migrate to the thymus. . Maturity of T-cells takes place in the thymus So, T cells arise in bone marrow and mature in thymus. 