Interferons are ...........

Arrange the steps of the $phagocytosis$ process in the correct sequence.
$(a)$ Ingestion of microbes by phagocytes
$(b)$ Dilation of blood vessels by histamine
$(c)$ Formation of $phagosome$ and $phagolysosome$
$(d)$ Migration of phagocytes into $E.C.F.$
$(e)$ Attraction of phagocytes by $chemotoxins$ secreted by microbes
$(f)$ Intracellular destruction of bacteria

Write a note on lymphoid organs.

In the list given below,how many are secondary lymphoid organs?
Thymus,Spleen,Bone marrow,Tonsil,Appendix

Passive immunity was discovered by

What is the main lymphoid organ where all blood cells including lymphocytes are produced?