Table 1.

The biological roles of HA of different molecular weights

HA fractions
HMW-HA (high molecular weight HA) molecular mass > 500 kDa, average mass 106–107 Da (~2000–25000 disaccharide units) [9, 73, 74]	LMW-HA (low molecular weight HA) molecular mass < 500 kDa (~1000 disaccharide units or less) [74 , 80]	O-HA (oligomeric HA) molecular mass 0.75—10 kDa (2 - 20 disaccharide units) [75]
Formation and stabilization of the structure of ECM and glycocalyx; immunologically inert [75, 76]; binds to cell receptors, prevents immune recognition; immunosuppressive action [77]; induction of Foxp3 expression, increases the number of inducible regulatory T-cells [77, 78]; preserves the barrier function of glomerular endothelial barrier [7] HA synthesis suppresses [74]	Functions as a danger signal (danger-associated molecular patterns) [9]; increases permeability of lymphatic capillaries [81], increases vascular permeability [7].	Can regulate various processes both positively and negatively; inhibit endogenous production of hyaluronan [9]
Anti-inflammatory action, inhibition of phagocytosis [77]	Anti-inflammatory action [33]
Anti-angiogenic effect, prevents transendothelial migration [77]	Pro-angiogenic effect, stimulation of endothelial cell proliferation, adhesion and formation of capillaries [33]	Stimulation/inhibition of angiogenesis, adhesion [9, 80]
Synthesis of immunosuppressive cytokines [77]	Synthesis of pro-inflammatory cytokines [33]
Stimulates proliferation and inhibits apoptosis of decidual stromal cells in early pregnancy [79]	Stimulates apoptosis of decidual stromal cells in early pregnancy [79]	Stimulation of tumor cell proliferation/ apoptosis [74]
Prevents adhesion and invasion of tumor cells [77]	Stimulation of tumor cell invasion and migration, stimulation of extravillous trophoblast cell invasion [82]