Table 1.

The basic information about hematopoietic and lymphopoietic activities in different lymphoid organs during prenatal ontogeny

Type of tissue	Establishment	Hemopoietic activity	First αβ T cells	First γδ T cells	First B cells	Basic germ layers	References
Yolk sack	12 DG - primordial	From DG16 to DG27	Not detected	Not detected	Only VDJH rearrangement detected	Endoderm	[8], [9], [25], [34]
	24 DG - functional capacity is finishing					Mesoderm
Liver	15 DG - primordial	From DG30 to the birth (decreasing)	DG58	DG45	DG30	Endoderm	[8], [9], [14], [25], [34]
	30–39 DG - invaded by hepatic cells					Mesoderm
Cord blood	15 DG - heart starts with pumping	–	DG58	DG45	DG40	–	[10], [34]
	28 DG - definitive coronary circulation
	55 DG - RBC are almost entirely enucleated
Spleen	20 DG - primordial	–	DG58	DG45	DG40	Mesoderm	[9], [10], [34]
	36 DG - complete formed
	36–114 DG - allometric growth
Thymus	22 DG - primordial	–	DG55	DG40	DG55	Endoderm	[10], [14], [25], [33], [34], [43]
	36 DG - complete formed					Ectoderm
	36–114 DG - allometric growth
MLN	55 DG - intestine complete in essential form	–	DG60	DG70 (always minor)	DG50	Mesoderm	[10], [34]
Bone marrow	18 DG - basically formed skeleton	From 45 DG to the birth (increasing)	DG60 (always minor)	DG60 (always minor)	DG55	Mesoderm	[6], [8], [9], [14], [25], [34]
	28 DG - ossification of bones

Occurrence of the first lymphocytes in different organs is based on flow cytometry studies detected by the expression of T and B cell receptors.