Association between Bacterial Virulence Factors and Host Immune Response: An Updated Review

  • Haneen Akram Habeeb1
  • Mohammed Flayyih Tareef2
  • Nihad Khalawe Tektook3
  • Shams Al-Mundhader Saad Abd4

Haneen Akram Habeeb1 , Mohammed Flayyih Tareef2 , Nihad Khalawe Tektook3 , Shams Al-Mundhader Saad Abd4

1Ministry of Education / General Directorate of Curricula, Baghdad, Iraq

2,3Middle Technical University / College of Health & Medical Techniques / Medical Laboratory Techniques, Baghdad, Iraq

3AL-Rasheed Secondary School for Girls, Rusafa District, Ministry of Education, Baghdad, Iraq

4Students at Kermanshah University of Medical Sciences, Kermanshah, Iran

Corresponding Author Email: Shamssaad@gmail.com

DOI : https://doi.org/10.51470/AMSR.2026.05.01.62

Abstract

Bacterial infections remain a major global health challenge, with disease outcomes determined by the dynamic interplay between bacterial virulent factors and host immune responses. Virulence determinants, including toxins, enzymes, and genetic elements, enable pathogens to invade host tissues, evade immune defences, and modulate host signalling pathways. In parallel, the host immune system responds through a complex network of innate and adaptive mechanisms, primarily mediated by cytokines such as IL-6, IL-17, and IL-23.
Recent evidence highlights that bacterial virulence factors not only promote infection but also actively shape immune responses, influencing inflammation, immune evasion, and disease progression. Dysregulation of this interaction may lead to excessive inflammation, tissue damage, or persistent infection. Moreover, advances in molecular and immunological techniques have provided new insights into host–pathogen interactions, enabling the identification of biomarkers and potential therapeutic targets.
This review provides an updated perspective on the association between bacterial virulence factors and host immune responses, emphasizing mechanistic interactions, clinical implications, and future research directions.

Keywords

Bacterial Virulence Factors, biomarkers, Host Immune Response, therapeutic targets

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1. Introduction

Bacterial infections remain a significant cause of morbidity and mortality worldwide, particularly in developing regions where infectious diseases continue to impose a heavy healthcare burden. The pathogenesis and clinical outcome of bacterial infections are largely determined by the interaction between bacterial virulence factors and the host immune response. These interactions are complex and dynamic, involving multiple microbial components and host defence mechanisms that collectively influence disease progression and severity.

Bacterial virulence factors play a central role in initiating and sustaining infection. These factors include structural components, toxins, enzymes, and genetic determinants that enhance bacterial survival and pathogenicity. For instance, studies on Staphylococcus aureus isolated from wound infections demonstrate the importance of bacterial properties in influencing infection outcomes and tissue damage [1]. Similarly, investigations on carbapenem-resistant Escherichia coli have shown that the presence of virulence genes is closely associated with host immune activation, particularly through modulation of cytokines such as interleukins (IL-6, IL-17, and IL-23) [2].

The host immune system, in turn, responds to bacterial invasion through a coordinated network of innate and adaptive mechanisms. Cytokines, particularly interleukins, play a pivotal role in mediating immune responses and regulating inflammation. Alterations in interleukin levels have been associated with inflammatory and infectious diseases, indicating their role as key mediators of immune defence [2,3]. Additionally, immunological markers such as TLR-7, IL-17A, and IL-10 highlight the broader significance of immune regulation in response to microbial challenges [4].

Importantly, the interaction between bacterial virulence factors and host immunity is bidirectional. While bacterial components can trigger immune activation, pathogens may also evade or suppress immune responses. Evidence from experimental studies on uropathogenic E. coli demonstrates that bacterial virulence factors can influence the development of protective immunity [5]. Furthermore, molecular and immunological diagnostic approaches have enhanced understanding of host–pathogen interactions [6].

Clinical studies further support the association between immune responses and disease outcomes. Neonatal bacterial septicemia has been linked to immune alterations and specific risk factors [7], while immunological biomarkers have been proposed for early diagnosis and prognosis [8].

In addition, immune responses influenced by microbial factors may contribute to systemic conditions. For example, bacterial infections have been associated with metabolic changes, such as alterations in lipid profiles [9], and Helicobacter pylori infection has been correlated with increased proinflammatory cytokines [10].

Bacterial Virulence Factors:

Bacterial virulence factors facilitate infection and influence disease progression by enabling pathogens to adapt to host environments and evade immune defences. The expression of virulence genes is often triggered upon host interaction, enhancing bacterial adhesion, invasion, and survival.

The association between virulence genes in carbapenem-resistant Escherichia coli and elevated cytokine levels (IL-6, IL-17, IL-23) highlights the direct link between bacterial factors and host immune activation [2]. Additionally, virulence factors contribute to immune evasion by modulating immune signalling pathways. Alterations in IL-10 and TLR-7 reflect immune modulation during infection and chronic conditions [4].

Excessive inflammation induced by virulence factors may contribute to tissue damage. Cytokines such as IL-6 are key mediators in inflammatory processes and are associated with disease complications [3]. Furthermore, virulence factors influence disease susceptibility, particularly in vulnerable populations such as neonates [7,8].

Bacterial virulence is also linked to systemic effects, including metabolic alterations and oxidative stress [3,9]. For example, Helicobacter pylori infection has been associated with increased inflammatory cytokines [10]. Molecular diagnostic techniques have further improved the detection of virulent genes and their clinical implications [6].

 Host Immune Response:

The host immune response is essential for controlling bacterial infections and involves complex interactions between cytokines, immune cells, and signalling pathways.

Cytokines such as IL-6, IL-17, and IL-23 are critical in mediating inflammation and immune activation [2]. However, excessive cytokine production may lead to tissue damage. Anti-inflammatory cytokines such as IL-10 help regulate immune responses and maintain balance [4].

Pattern recognition receptors such as TLR-7 play a key role in detecting pathogens and initiating immune responses [4]. Clinical evidence shows that immune responses significantly influence disease outcomes, particularly in neonatal infections where immune immaturity increases susceptibility [7,8].

Chronic infections, such as Helicobacter pylori, are associated with sustained immune activation and inflammation [10]. Additionally, immune responses may influence systemic physiological processes, including oxidative stress and metabolic changes [3,9].

Protective immunity can also develop following exposure to bacterial virulence factors, as demonstrated in studies on uropathogenic E. coli [5]. This highlights the dual role of immune responses in both protection and pathology.

3. Host Immune Response to Bacterial Infection

  • Innate immunity
  • Cytokines (IL-6, IL-17, IL-10)
  • Immune regulation

4. Mechanistic Interaction Between Virulence and Immunity:

The interaction between bacterial virulence factors and the host immune response is a highly dynamic and tightly regulated process that determines the outcome of infection. Mechanistically, bacterial pathogens not only trigger immune activation but also actively manipulate host immune pathways to enhance their survival and persistence.

A key mechanism involves modulating cytokine signalling. Bacterial virulence factors, such as those from Escherichia coli, are associated with increased levels of proinflammatory cytokines, including IL-6, IL-17, and IL-23 [2]. These cytokines are essential for recruiting immune cells and amplifying inflammation. However, excessive cytokine production can lead to tissue damage and worsen disease severity. This suggests that bacterial virulence factors may trigger a transition from protective immune responses to harmful inflammation.

Bacterial pathogens not only promote inflammation but also employ sophisticated immune-evasion strategies. Some virulence factors disrupt host immune signalling pathways, particularly those mediated by Toll-like receptors (TLRs). Alterations in TLR-7 expression, together with changes in cytokines such as IL-10, indicate that pathogens can suppress or modulate immune responses to avoid detection and clearance [4]. This immune modulation enables bacteria to establish persistent infections and evade host defences.

Another important factor is the balance between proinflammatory and anti-inflammatory responses. Cytokines like IL-6 and IL-17 are involved in pathogen clearance, whereas anti-inflammatory cytokines such as IL-10 help regulate immune activity and reduce tissue damage. When this balance is disrupted—often by bacterial virulence factors—it can result in uncontrolled infections or chronic inflammation [4]. For example, in neonatal septicemia, the immature immune system combined with bacterial virulence can cause either an excessive or insufficient response, significantly affecting disease outcomes [7,8].

Additionally, bacterial virulence factors can affect host metabolic and oxidative pathways, indirectly shaping immune responses. Research shows a connection between inflammatory cytokines and oxidative stress markers like malondialdehyde (MDA), suggesting that immune activation is tightly connected to cellular stress responses [3]. This interaction underscores the systemic effects of bacterial infections beyond localized immune responses.

Chronic infections provide additional insight into these mechanisms. For instance, Helicobacter pylori infection has been associated with sustained elevation of proinflammatory cytokines, particularly IL-17, contributing to chronic inflammation and disease progression [10]. This suggests that certain virulence factors promote long-term immune activation. Importantly, the interaction between bacterial virulence factors and the immune system is not solely detrimental. In some cases, exposure to virulence determinants can stimulate protective immune responses. Experimental studies on uropathogenic E. coli have demonstrated that virulence-associated antigens can induce immune memory and enhance resistance to subsequent infections [5]. This dual role underscores the complexity of host–pathogen interactions.

Overall, these findings indicate that bacterial virulence factors act as key modulators of host immune responses through multiple interconnected mechanisms, including cytokine induction, immune evasion, regulation of inflammation, and metabolic interactions. Understanding these mechanisms in depth is essential for developing targeted therapies that simultaneously inhibit bacterial virulence and modulate host immune responses.

  • The interaction between bacterial virulence factors and host immune responses represents a critical determinant of disease outcomes, extending beyond simple pathogen recognition. The findings discussed in this review highlight that bacterial virulence is not a static property, but rather a dynamic process influenced by the host.
  • Mechanistically, the correlation between virulence genes and cytokine production suggests that pathogens actively shape immune responses rather than merely triggering them. Elevated levels of IL-6, IL-17, and IL-23 reflect a proinflammatory environment that is essential for pathogen clearance but may also contribute to tissue damage when dysregulated [2].
  • Importantly, immune evasion emerges as a central strategy employed by bacteria. The modulation of immune pathways, including TLR signalling and anti-inflammatory cytokines such as IL-10, demonstrates how pathogens can suppress host [4]. This suggests that successful pathogens are those that can fine-tune host immune responses rather than completely evade detection.
  • Clinical evidence further supports this concept. In neonatal septicemia, for example، the interplay between immature immunity and bacterial virulence leads to unpredictable and often severe outcomes [7,8]. Similarly, chronic infections such as Helicobacter pylori illustrate how persistent immune activation can drive long-term pathology through sustained cytokine production [10].
  • Another key insight is the systemic impact of host–pathogen interactions. The association between immune responses and metabolic or oxidative pathways, such as the relationship between IL-6 and MDA, indicates that bacterial infections can influence broader physiological processes [3].
  • From a translational perspective, these findings highlight the potential of targeting both bacterial virulence factors and host immune pathways. Traditional antimicrobial therapies focus primarily on bacterial eradication; however, emerging strategies aim to modulate immune responses or inhibit virulence mechanisms, thereby reducing tissue damage and limiting disease progression.

7. Future Perspectives:

Future research should focus on integrating molecular, immunological, and clinical data to understand host–pathogen interactions better. The identification of specific virulence factors that directly influence immune signalling pathways could lead to the development of targeted therapies that disrupt these interactions.

Additionally, the use of immunological biomarkers such as cytokines offers promising opportunities for early diagnosis and prognosis of bacterial infections. Advances in molecular diagnostics and genomic analysis will further enhance the ability to detect virulence genes and predict disease outcomes.

Another important direction is the development of immunomodulatory therapies that can restore immune balance without compromising pathogen clearance. This approach may be particularly beneficial in conditions characterized by excessive inflammation, such as sepsis and chronic infections.

Finally, a systems biology approach combining immunology, microbiology, and bioinformatics will be essential to understand the complexity of host–pathogen interactions fully and to develop personalised treatment strategies.

8. Conclusion

The interaction between bacterial virulence factors and host immune responses plays a central role in the pathogenesis of infectious diseases. Virulence determinants not only facilitate bacterial survival and invasion but also actively modulate host immune pathways, shaping both protective and pathological responses.

Emerging evidence suggests that this relationship is highly dynamic, with bacteria influencing cytokine signalling, immune cell activation, and inflammatory balance. While effective immune responses are essential for pathogen clearance، dysregulated responses can lead to chronic inflammation أو tissue damage.

Understanding this interplay at a mechanistic level is crucial for developing innovative therapeutic strategies that target both microbial virulence and host immune modulation. Future research should focus on integrating molecular, immunological, and clinical data to identify novel biomarkers and to improve personalized approaches to the management of bacterial infections.

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  2. Tektook NK, Mohammed Al-Warmeziary MA, Hussain SS. Correlation between serum levels of interleukins (IL-6, IL-17 and IL-23) and virulence genes detected in carbapenem-resistant Escherichia coli. Indian J Forensic Med Toxicol. 2020;14(2):2485–2491.
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