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.
IFN alpha
TNF alpha
IL-1
IL-6