Azithromycin (AZM), primarily recognized for its antibiotic properties, has gained attention for its ability to modulate the immune system and reduce inflammation. This review explores the impact of AZM on various immune cell types, including T cells, B cells, and natural killer (NK) cells, and its potential in treating chronic inflammatory and autoimmune conditions. AZM inhibits the mTOR signaling pathway in T cells, thereby limiting both T cell proliferation and cytokine production. It also affects B-cell function by modulating pathways such as NF-κB and CD27, thereby influencing antibody synthesis. In NK cells, AZM reduces cytotoxicity and cytokine release while preserving cell viability. The drug’s effects on immune responses, particularly on vaccination responses and reduced antibody levels, have important clinical implications. While AZM shows potential for managing conditions such as graft-versus-host disease and asthma, its varied effects highlight the need for further investigation. Further understanding of these mechanisms is crucial for optimizing AZM’s therapeutic use and minimizing unwanted immune suppression.
Azithromycin (AZM), a member of the azalide subclass of macrolide antibiotics, is widely prescribed worldwide for the treatment of bacterial infections [1]. In the United States, it ranks second among antibiotics, with nearly 35 million prescriptions dispensed in 2022 alone [2]. Its widespread use is attributed to several advantageous features, including broad-spectrum antimicrobial activity against gram-positive, gram-negative, and atypical organisms; efficient tissue distribution; strong accumulation in macrophages; a prolonged half-life; short treatment courses; and, notably, its anti-inflammatory properties [1].
The anti-inflammatory potential of AZM has sparked growing scientific interest, particularly for conditions beyond its traditional role in infectious diseases. Investigations are currently exploring its therapeutic value across various domains, including respiratory illnesses, autoimmune disorders, cancer treatment, and COVID-19 management [3–7]. Despite these promising directions, findings regarding AZM’s anti-inflammatory properties remain inconclusive and, at times, contradictory. Ongoing debate surrounds the extent and consistency of its benefits in non-infectious inflammatory diseases, as misconceptions and exaggerated claims have emerged in both clinical and research contexts.
Given these challenges, there is a pressing need for a critical, systematic evaluation of the literature to distinguish evidence-based effects from mere speculation. By examining the current peer-reviewed literature, this review aims to clarify the biological mechanisms by which AZM modulates immune responses. Such clarity will support improved study designs, reduce unnecessary experimentation, and ensure more effective use of scientific and medical resources. Ultimately, this work seeks to strengthen the understanding of AZM’s immunomodulatory role and inform its future therapeutic applications.
Rapamycin (also known as sirolimus) is a macrocyclic lactone first isolated in 1964 from soil collected on Easter Island (Rapa Nui), produced by the bacterium Streptomyces hygroscopicus. Initially investigated for its antifungal properties due to its lack of antibacterial effects [8, 9], rapamycin later attracted attention for its potent ability to suppress the growth of eukaryotic cells. This led to the identification of its molecular target—TOR (target of rapamycin) in yeast—and eventually to the discovery of its mammalian equivalent, mTOR. Rapamycin binds to FK506-binding protein 12 (FKBP12), forming a complex that inhibits mTOR activity. This inhibition effectively blocks T-cell activation, proliferation, and cytokine production, making it a key immunosuppressant in transplant medicine [9, 10].
Given rapamycin’s success, researchers turned their focus to other macrolides—particularly Azithromycin (AZM)—to investigate whether similar mTOR-inhibitory effects might exist.
Ratzinger and colleagues [11] were among the first to demonstrate that AZM significantly reduces lymphocyte proliferation and cytokine output in a dose-dependent manner. These effects were attributed to its ability to inhibit mTOR. Since the mTOR pathway plays a pivotal role in T-cell growth, survival, differentiation, and autophagy [10], AZM’s inhibition of this pathway was a notable finding. Compared to clarithromycin, AZM showed a more potent suppressive effect.
In their study, Ratzinger et al. [11] used isolated human T cells from 10 healthy volunteers and recombinant mTOR kinase fragments to provide direct evidence of mTOR inhibition. They confirmed that AZM directly inhibits mTOR kinase activity, with suppression observed both in the presence and absence of FKBP12. For comparison, 500 nM of rapamycin (used as a control) reduced mTOR activity by 67.3% (P < 0.001) only when FKBP12 was present. In contrast, AZM at 1000 mg/L reduced mTOR activity by 31.5% (P < 0.001) with FKBP12 and by 27% (P < 0.001) without it [11].
Additionally, the study ruled out AZM’s indirect effect on mTOR through the phosphoinositide 3-kinase (PI3-K) pathway. No significant inhibition of PI3K was observed (P = 0.6267), supporting the conclusion that AZM acts directly on mTOR rather than via upstream signaling.
Further findings by Weng et al. [12] showed that higher AZM concentrations (40 mg/L) significantly compromised cell viability, reducing it by almost half compared with controls. At the same time, lower doses had a negligible impact on survival. Clarithromycin did not show similar cytotoxic effects at the tested levels [12].
As summarized in Table 1, several studies support the idea that AZM’s mTOR inhibition is primarily driven by suppression of S6 ribosomal protein (S6RP) phosphorylation, a downstream indicator of mTOR pathway activity [11–14]. Moreover, Ansari et al. [14] explored the detailed molecular mechanisms by which AZM disrupts T-cell function, and Bergström et al. [15] contrasted AZM’s immunosuppressive effects with those of rapamycin, further contextualizing its potential as a modulator of T-cell activity.
Table 1. Overview of key studies investigating azithromycin’s impact on the mTOR pathway
Study | Main findings |
Ratzinger et al. [11] | Demonstrated that AZM reduced CD4+ T-cell proliferation and cytokine production in a dose-responsive fashion. |
Weng et al. [12] | Found that AZM strongly suppressed T-cell growth, induced apoptosis, and increased autophagosome development in T lymphocytes. |
Huang et al. [13] | Reported that AZM elevated Treg populations while reducing effector T cells. It also inhibited CD4+ T-cell proliferation and activation, promoting cell death in CD4+CD44+ memory T cells and CD4+CXCR3+ Th1 subsets. |
Ansari et al. [14] | Observed that AZM significantly limited T-cell expansion and downregulated ICOS and OX40, key costimulatory surface proteins. |
Bergström et al. [15] | Noted that AZM, like rapamycin, supported the development of FoxP3-expressing T regulatory cells, though rapamycin-treated Tregs showed stronger suppressive capacity. |
The effects of azithromycin (AZM) on natural killer (NK) cells remain relatively underexplored. However, a recent investigation examined how AZM influences NK cell functions, including activation, apoptosis, and cytotoxicity. The study found that AZM, at clinically relevant concentrations, did not compromise NK cell viability. Nevertheless, it significantly reduced IL-15-induced CD69 expression in a dose-dependent manner. CD69 serves as an early marker of NK cell activation and plays a vital role in modulating their immune function.
Additionally, AZM diminished the cytolytic ability of both resting and IL-15-activated primary NK cells when challenged with K562 target cells. This reduction in cytotoxic activity was attributed to decreased perforin expression, a key molecule in NK cells that induces cell death in target cells by facilitating granzyme entry. Notably, NK cell subsets expressing CD16 and CD56—typically associated with higher perforin levels—were more vulnerable to AZM’s suppressive effects than CD16−CD56+ subsets.
Furthermore, AZM inhibited the secretion of IFN-γ and TNF-α in NK-92 cells, a cell line derived from a malignant NK tumor that naturally produces these cytokines. However, no such suppression was observed in IL-15-activated primary NK cells. These results indicate that AZM can modulate NK cell activity—including cytotoxicity and cytokine production—without impairing their survival. Such modulation could offer clinical benefits in treating conditions marked by excessive NK cell activity, such as asthma or chronic inflammation. Additional studies are warranted to clarify the clinical relevance and therapeutic potential of AZM’s effects on NK cells [16].
Azithromycin also affects B cells by interfering with critical signaling cascades that regulate their development and immune functions. One of the main pathways impacted by AZM is the NF-κB pathway—a central transcriptional regulator that governs B-cell proliferation, activation, and longevity [17]. AZM inhibits NF-κB activation, potentially curbing B-cell responsiveness and limiting their ability to generate antibodies [18].
Beyond NF-κB, AZM also influences the CD27-CD70 signaling axis. CD27, a member of the tumor necrosis factor receptor family, is instrumental in regulating B-cell activation and the transformation of B cells into plasma cells—the antibody-secreting subset. By interfering with CD27-mediated signaling, AZM may hinder the differentiation of B cells into plasma cells, ultimately reducing antibody production [19, 20].
Overall, AZM’s effects on B cells represent a nuanced modulation of multiple immune pathways. While its suppressive action on B-cell function could prove advantageous in autoimmune or hyperinflammatory conditions, it also raises concerns about impaired humoral immunity. Understanding how AZM’s influence on B cells varies across treatment settings and patient groups is critical for maximizing its clinical benefits while minimizing immune-related risks.
Table 2 outlines the findings from various studies investigating the influence of azithromycin (AZM) on immunoglobulin E (IgE) levels across different models.
Table 2. Overview of studies examining AZM’s effects on IgE levels
Study | Model | Observed effect on IgE |
Wang et al. [21] | Mouse | No noticeable change |
Tkalčević et al. [22] | Mouse | Reduction in serum IgE |
Hahn et al. [23] | Human | No effect observed |
Borbet et al. [24] | Mouse | Elevated serum IgE levels |
Smith-Norowitz et al. [25] | Human (observational) | Increase at low doses, decrease at high doses |
Tiotiu et al. [26] | Human (observational) | No change detected |
Wan et al. [27] | Rat | No change observed |
Ni et al. [28] | Human (combined with ambroxol) | Decrease in serum IgE |
Kang et al. [29] | Mouse | Lowered serum IgE levels |
While the overall data on AZM’s influence on IgE levels appear contradictory, the general trend suggests minimal or inconsistent impact on serum IgE concentrations. The disparity in findings may be attributed to the frequent focus on asthma in AZM-related research—a condition commonly linked with IgE-mediated mechanisms. Some studies report no influence on asthma exacerbations, whereas others suggest potential therapeutic value under specific conditions [30–32].
The Global Initiative for Asthma currently supports the use of low-dose AZM as an add-on treatment in cases of severe asthma to help reduce the frequency of exacerbations [33].
An additional consideration is the potential of AZM to trigger IgE-mediated hypersensitivity. A longitudinal pediatric study found that AZM was significantly more allergenic than clarithromycin, with nearly 50% of children showing positive responses to skin or oral challenge tests. The study reported a 75% positive predictive value for AZM-specific IgE. Airborne sensitization has also been documented, particularly in pharmaceutical workers who developed allergic contact dermatitis. However, allergic reactions to macrolides like AZM remain rare, with an estimated prevalence of 0.4%–3% [34].
Interestingly, AZM may also exert a protective role against hypersensitization. Research by Fillaux et al. [35] showed that children who had never been exposed to AZM were 1.9 times more likely to develop sensitization to Aspergillus fumigatus compared to those who had received the antibiotic.
These findings highlight the complexity of AZM’s immunological effects, particularly on IgE levels. Further investigation is required to clarify its role across various disease settings and patient populations.
Table 3 summarizes investigations into AZM’s effects on different antibody classes, revealing inconsistent outcomes.
Table 3. Summary of studies on AZM’s effects on other antibody types
Study | Antibody type | Outcome |
Smith-Norowitz et al. [25] | IgG, IgM | No significant change |
Ni et al. [28] | IgG | Decrease in combination with ambroxol |
Hahn et al. [23] | IgA, IgG | No effect reported |
Fillaux et al. [35] | IgE (Aspergillus-specific) | Reduced the sensitization rate |
Tiotiu et al. [26] | IgG | No impact observed |
Overall, these findings suggest that azithromycin does not consistently or significantly affect overall antibody production. The variability in results may reflect differences in underlying conditions, treatment durations, or population characteristics. Moreover, there is currently limited data on how AZM may influence immunoglobulin D (IgD), leaving an essential gap in our understanding of its broader immunomodulatory potential [36-40].
Fernandez et al. [41] demonstrated that azithromycin (AZM) significantly reduced antibody levels in mice vaccinated with 100 µL of the 7-valent pneumococcal conjugate vaccine (PCV7) when compared to untreated controls. In contrast, neither ceftriaxone nor ciprofloxacin had a notable effect on the total antibody response to this vaccine. The observed reduction in immune response, particularly in total antibody levels, was mainly attributed to decreased concentrations of the IgG1 subclass. In a related investigation, Woo et al. [42] reported that clarithromycin treatment in mice reduced total antibody levels following immunization with a pneumococcal polysaccharide vaccine. The reduction was primarily in IgM levels, while IgG1 remained unaffected. This difference in immunoglobulin response may be due to the type of antigen used: Woo et al. used a T-cell–independent antigen, while Fernandez et al. used a T-cell–dependent formulation.
Another study by Borkner et al. [43] found that AZM was effective in eradicating Bordetella pertussis infection in mice. However, this therapeutic benefit was accompanied by a significant reduction in both innate and adaptive immune responses in the lungs. Specifically, AZM-treated mice showed decreased CD4+ T-cell responses and reduced bacterial clearance when compared to untreated mice immunized with a whole-cell pertussis vaccine. These findings raise concerns that AZM could interfere with immune system responses to vaccination. Although the clinical implications of these results remain unclear, current medical guidelines advise against administering vaccines during an active infection. This suggests that vaccination should ideally be postponed during any antibiotic treatment, particularly with AZM. Additionally, in patients requiring long-term AZM therapy—such as those with chronic obstructive pulmonary disease (COPD)—the timing and effectiveness of vaccinations should be carefully considered [44].
Due to its unique immunomodulatory and antimicrobial properties, AZM has been explored in the treatment of various diseases, although its benefits are not consistently significant across all conditions.
In the field of hematology, promising results have emerged from a study by Ozkan et al. [45], who found that AZM, whether used alone or in combination with imatinib, was particularly effective against imatinib-resistant chronic myeloid leukemia (CML) stem cells. This suggests AZM may hold potential as an anti-leukemic agent.
Additional research has focused on using AZM to treat mucosa-associated lymphoid tissue (MALT) lymphoma, especially in cases linked to Helicobacter pylori infection. AZM’s potential to treat both the underlying disease and the lymphoma itself makes it an appealing therapeutic candidate. In a phase II clinical trial conducted by Lagler et al. [46], AZM was administered at a dose of 1500 mg and was generally well tolerated. However, its effectiveness was limited, with only 2 patients achieving complete remission and another 2 showing partial remission out of 16 participants. Despite these modest results, AZM’s role in lymphoma therapy warrants further investigation.
AZM has also been studied as a supportive treatment for graft-versus-host disease (GVHD). Some evidence suggests it can influence immune regulation by boosting T regulatory cell activity and shifting the balance between Th1 and Th2 cells, potentially helping reduce inflammation. Iwamoto et al. [47] reported that AZM prevented fatal GVHD in mice, likely by suppressing NF-κB signaling. Another murine study supported this conclusion, citing a reduction in the expansion of intestinal T cells as the mechanism of action [48]. However, these positive outcomes in animal models were not replicated in a randomized controlled trial in humans, which did not demonstrate significant therapeutic benefit for AZM in GVHD treatment [49].
Azithromycin (AZM) has garnered attention for its anti-inflammatory effects in autoimmune diseases. In systemic lupus erythematosus (SLE), AZM has been shown to promote macrophage polarization toward the M2 phenotype, associated with anti-inflammatory activity and enhanced tissue repair. Experimental lupus models have demonstrated that AZM reduces hallmark disease indicators, such as anti-dsDNA antibody levels, serum creatinine, and kidney tissue damage [6].
In rheumatoid arthritis, AZM’s role extends beyond infection control. It has been shown to suppress the production of pro-inflammatory cytokines and influence immune-related signaling pathways. One notable mechanism involves its interaction with glucose-regulated protein 78 (GRP78), which plays a role in AZM’s anti-arthritic actions. This interaction affects various metabolic pathways, including those governing lipid and cholesterol synthesis, which are frequently disrupted in autoimmune disorders. Additionally, AZM has been shown to reduce migration, invasion, and programmed cell death in fibroblast-like synoviocytes, suggesting it may effectively hinder disease progression [4].
Emerging evidence also supports AZM’s therapeutic potential in autoimmune-related complications such as radiation-induced lung injury (RILI). In this setting, AZM’s immunomodulatory actions—including suppression of neutrophil infiltration, regulation of autophagy, and modulation of macrophage responses—help limit inflammation and tissue fibrosis [5].
Overall, AZM’s repurposing for autoimmune diseases builds on its well-documented safety profile and multifaceted immunological effects. By targeting key pathways of inflammation and immune dysregulation, AZM could become a promising adjunct in the management of autoimmune disorders.
Recent investigations suggest that AZM may interfere with the interaction between SARS-CoV-2 and the CD147 receptor, potentially curbing viral replication in hospitalized patients. CD147, like ACE2, serves as an entry point for the virus into host cells. AZM has also been shown to downregulate metalloproteinase expression triggered by CD147 activation, which may, in turn, boost antiviral responses in bronchial epithelial cells infected with rhinovirus. Moreover, AZM may help protect against pulmonary fibrosis in COVID-19 by preserving lung progenitor and stem cells, although further clinical trials are needed to confirm these effects [50].
Another review highlights AZM’s ability to enhance antiviral immunity by promoting type I interferon production. It may also regulate excessive inflammation by decreasing pro-inflammatory cytokines and modulating macrophage responses. Furthermore, AZM might influence the activity of neutrophils and T cells, helping to dampen the hyperinflammatory state seen in severe cases of COVID-19. Continued research is essential to understand better its full therapeutic potential in managing the disease [7].
AZM’s broad immunomodulatory impact on immune cells makes it a strong candidate for novel therapeutic applications, particularly in managing inflammation-related conditions. These properties not only support its effectiveness in treating severe infections but also open the door for developing new antibiotic agents that mimic AZM’s dual action.
One of AZM’s strengths lies in its favorable safety profile. It is generally well tolerated, with few patients requiring discontinuation of treatment due to side effects. Compared to other macrolides, AZM is associated with fewer cardiovascular complications [1]. It also outperforms erythromycin in treating diffuse panbronchiolitis, due to its faster onset of action, longer post-antibiotic effects, fewer drug interactions, and better patient adherence. Although both are used for this condition, AZM offers distinct advantages in safety and therapeutic effectiveness [12].
However, the emergence of bacterial resistance remains a significant concern, particularly given AZM’s continued widespread use. This highlights the need for prudent use and ongoing research into mechanisms of resistance. Despite this, AZM’s rare combination of anti-infective and anti-inflammatory actions, coupled with a strong safety profile, makes it a valuable therapeutic agent. Further studies aimed at reducing resistance and expanding its clinical applications could enhance its role in treating both infectious diseases and immune-mediated conditions.
Azithromycin (AZM) stands out as a therapeutic agent due to its combined antimicrobial and anti-inflammatory effects, along with its well-established safety record. These attributes make it particularly useful in addressing both infectious and inflammatory conditions. While the growing threat of antibiotic resistance warrants caution, AZM’s distinctive therapeutic advantages remain compelling. Continued investigation into resistance pathways and emerging clinical uses will be vital to sustaining its relevance in the treatment of multifaceted diseases.
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