Body size and infection: An immunological balancing act

Table 1 Average size of various microbes and human cells and their biology

Structure	Approximate size	Role in homeostasis and immunity	Ref.
Small molecules (cytokines, hormones)	1-50 kDa	Immune signaling, metabolic regulation	[6]
Antibodies	Approximately 150 kDa	Pathogen neutralization, immune memory	[6]
Viruses	20-300 nm	Intracellular infection, immune evasion	[5]
Bacteria	0.2-10 μm	Commensals and pathogens	[5]
Fungi	2-10 μm (yeasts), > 50 μm (hyphae)	Opportunistic infections, host-microbe interactions	[5]
Protozoa	10-50 μm	Parasitic infections	[5]
Helminths	mm to meters	Chronic infections, immune modulation	[5]
Cells (e.g., macrophages, neutrophils)	10-50 μm	Immune surveillance, pathogen elimination	[7]
Mucosal and skin barriers	Approximately 2 m2 (skin), approximately 400 m2 (mucosa)	First-line defense against infections	[27]
Blood and lymphatic surface areas	Approximately 3000 m2 (capillary endothelium)	Circulation and immune trafficking	[27]