Interleukin secreted by macrophages, stimulating lymphocytes is

IL1> IL6 Macrophages release IL – 1 which stimulates the T – helper cells. The T – cells in response proliferate and release IL – 2 which in turn further stimulates T – cell proliferation and B cell proliferation and differentiation into plasma cells. Please note that even IL-6 (produced by macrophages) acts on late stages of B cell differentiation enhancing antibody formation. Still, IL-1 being the most important cytokine having systemic effects of inflammation has been chosen as the answer here in preference to IL-6.