Host Immune Response to E. Coli

 Innate Immune Response Against Pathogenic E. Coli

 

The innate immune system provides immediate, nonspecific protection against E. coli infection. The gastrointestinal tract (GIT) forms the first line of defence through chemical and physical barriers. In healthy individuals, gastric acidity (pH ~1.5) is a key factor, cause E. coli can only survive for a few hours in pH 2–3 (Martinson & Walk, 2020). Thus, gastric acid serves as a significant barrier (Martinsen et al., 2005). Additional defences include the impermeable inner mucus layer, the colon's thickness, and intestinal motility, which aid in pathogen clearance (Gieryńska et al., 2022). If E. coli bypasses these defences, pattern recognition receptors (PRRs) detect it. Toll-like receptor 4 (TLR4) recognises the lipopolysaccharide (LPS) on the bacterial outer membrane (Backhed et al., 2001), while TLR5 detects flagellin, a structural protein of bacterial flagella (Hayashi et al., 2001). These interactions activate immune cells such as neutrophils and macrophages, leading to the release of proinflammatory cytokines like interleukin-1β (IL-1β) and tumour necrosis factor-alpha (TNF-α) (Kaper et al., 2004). In addition, the complement system may promote bacterial lysis.

 

Adaptive Immune Response Against Pathogenic E. Coli

 

The adaptive immune system activates by providing unique and long-lasting protection if the innate immune system is unable to eliminate the infection. When professional antigen-presenting cells transmit an antigen, T-helper cells are activated, starting a chain of immunological reactions.  Immunoglobulin A (IgA) targets colonisation factor antigens (CFAs) in mucosal defence and heat-labile toxin (LT) infections caused by ETECs (Akhtar et al., 2023). Same as IgA, immunoglobulin G (IgG) serves as one of the key factors of immune defence. The infection progress is affected by the cytokine profile of activated T-helper cells, such as Interleukin-4 (IL-4), interferon-gamma (IFN-γ), and interleukin-10 (IL-10) (Long et al., 2009). B lymphocytes can balance gut bacteria besides producing antibodies. Depending on the reactions, the pathogen may be eliminated more quickly or slowly. Memory cells are produced after initial exposure to the pathogen, which helps the immune system respond to re-infection more quickly and efficiently.