Phytochemistry, Mechanisms, and Preclinical Studies of Echinacea Extracts in Modulating Immune Responses to Bacterial and Viral Infections: A Comprehensive Review

Abstract

Background: Echinacea species, particularly Echinacea purpurea, Echinacea angustifolia, and Echinacea pallida, are renowned for their immunomodulatory, antibacterial, and antiviral properties.

Objectives: This review explores the mechanisms by which echinacea herbal extracts modulate immune responses, focusing on their effects on both innate and adaptive immunity in bacterial and viral infections.

Results: Key bioactive compounds, such as alkamides, caffeic acid derivatives, flavonoids, and polysaccharides, contribute to these effects. These compounds enhance immune cell activity, including macrophages and natural killer cells, stimulating cytokine production and phagocytosis. The antibacterial activity of echinacea against respiratory pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Legionella pneumophila) and skin pathogens (Staphylococcus aureus, Propionibacterium acnes) is reviewed, as well as its antiviral efficacy against viruses like herpes simplex, influenza, and rhinovirus. Echinacea's potential as a complementary treatment alongside conventional antibiotics and antivirals is discussed, particularly in the context of antibiotic resistance and emerging viral threats.

Conclusions: Challenges associated with variability in phytochemical content and the need for standardized extraction processes are also addressed. This review provides a comprehensive overview of echinacea's therapeutic potential and outlines future directions for research, including clinical trials and dosage optimization.

Keywords: COVID-19; alkamides; caffeic acid derivatives; immune system; medicinal plant; phytochemistry.

Figure 1

Botanical illustration of E. purpurea, depicting the aerial and root structures (Figure drawn by F. Ahmadi).

Figure 2

Structure of the main echinacea alkamides (Figure drawn by F. Ahmadi).

Figure 3

Flavonoids found in echinacea species (Figure drawn by F. Ahmadi).

Figure 4

A possible biosynthesis pathway for chicoric acid and caffeic acid is derived via the phenylpropanoid pathway in echinacea species. PAL: phenylalanine ammonia-lyase, C4H: cinnamate-4-hydroxylase, C3H: coumarate 3-hydroxylase, 4CL: 4-coumarate-CoA ligase, HCT: shikimate o-hydroxycinnamoyl transferase (Figure drawn by F. Ahmadi).

Figure 5

Antiviral activity of echinacea extract against SARS-CoV-2 virus (Figure drawn by F. Ahmadi).

Figure 6

A schematic representation of the main molecular pathways linked to inflammatory and immunomodulatory activities modulated by echinacea. The solid red line indicates the pathway’s activation, whereas the truncated red line indicates inhibition of the pathway. TLR-4: Toll-like Receptor-4; MyD88: Myeloid Differentiation Primary Response 88; NF-KB: Nuclear Factor kappa B; MAPK: Mitogen-Activated Protein Kinase; COX-2: cyclooxygenase-2; iNOS: inducible Nitric Oxide Synthase; HO-1: Heme Oxygenase-1; IL: Interleukin; TNF: Tumor Necrosis Factor (Figure drawn by F. Ahmadi).