The relationship between testosterone Immune VitalisLuxe and the immune system is one of the most biologically fascinating and clinically underappreciated aspects of male hormonal health. Most men think of testosterone in terms of libido, muscle, and energy — but testosterone is also a significant modulator of immune function, inflammatory signalling, and the body’s susceptibility to both infection and chronic inflammatory disease.
At Vitalis Luxe Clinic in Hull, men increasingly arrive having connected their low testosterone with a broader pattern of feeling unwell — recurrent infections, persistent fatigue that does not respond to sleep, or inflammatory conditions that have flared alongside hormonal decline. This article explains the testosterone-immune relationship, what it means clinically, and what the evidence shows about TRT’s immunomodulatory effects.
Table of Contents
Testosterone as an Immunomodulator
Testosterone acts on immune cells directly through androgen receptors expressed throughout the immune system — on T lymphocytes, B lymphocytes, natural killer (NK) cells, dendritic cells, macrophages, and neutrophils. This means testosterone has direct regulatory effects on immune cell function — not just indirect effects through general health and metabolic status.
The overarching character of testosterone’s immune effect is immunomodulatory and anti-inflammatory — it tends to dampen excessive immune activation, reduce pro-inflammatory cytokine production, and support immune tolerance. This is why men generally have stronger, more aggressive initial immune responses than women (oestrogen promotes immune reactivity) but also why men have substantially lower rates of autoimmune disease — conditions in which the immune system attacks the body’s own tissues. The testosterone-oestrogen balance is a primary determinant of the sex difference in autoimmune susceptibility.
How Testosterone Affects Specific Immune Functions
Immune Parameter | Effect of Adequate Testosterone | Effect of Testosterone Deficiency |
|---|---|---|
Pro-inflammatory cytokines (TNF-alpha, IL-6, IL-1beta) | Suppressed — testosterone reduces production of these key inflammation mediators | Elevated — testosterone deficiency is associated with raised CRP, IL-6, and TNF-alpha; chronic low-grade inflammation |
T regulatory cells (Tregs) | Supported — testosterone promotes Treg differentiation; Tregs suppress excessive immune activation and autoimmunity | Reduced Treg function — contributes to increased autoimmune susceptibility in low-testosterone states |
Natural killer (NK) cell activity | Modulated — testosterone has complex effects on NK cell cytotoxicity; broadly maintains appropriate NK surveillance | Altered NK function — may impair tumour and viral surveillance |
Neutrophil function | Supported — testosterone supports neutrophil bactericidal activity | Reduced — chronic testosterone deficiency may impair innate immune first-responder function |
B lymphocyte activity | Partly suppressed — testosterone reduces excessive B cell antibody production; one mechanism reducing autoimmune antibody generation | Increased B cell activity — higher autoantibody production risk |
Macrophage polarisation | Promotes anti-inflammatory M2 macrophage phenotype | Promotes pro-inflammatory M1 macrophage phenotype — contributes to chronic tissue inflammation |
CRP / inflammatory markers | Maintained in low-normal range | Significantly elevated CRP, IL-6, fibrinogen in hypogonadal men — equivalent inflammatory burden to metabolic syndrome |
Testosterone Deficiency and Chronic Inflammation
One of the most clinically significant immunological consequences of testosterone deficiency is chronic systemic inflammation — elevated circulating levels of pro-inflammatory cytokines and acute-phase proteins (particularly CRP, IL-6, and TNF-alpha) that persist in the absence of acute infection or injury. This chronic low-grade inflammatory state is not merely a laboratory finding — it is a recognised driver of multiple chronic diseases:
- Accelerated atherosclerosis and cardiovascular disease — chronic inflammation is a key pathophysiological driver of plaque formation and destabilisation
- Insulin resistance and type 2 diabetes — inflammatory cytokines (particularly TNF-alpha) directly impair insulin signalling in muscle and liver
- Osteoporosis — inflammatory cytokines stimulate osteoclast activity, accelerating bone resorption
- Depression and cognitive decline — neuroinflammation from elevated systemic cytokines contributes to mood disruption and cognitive impairment
- Cancer risk — chronic inflammation is a recognised promoter of carcinogenesis through multiple mechanisms including DNA damage and impaired immune surveillance
Studies show that TRT in hypogonadal men reduces CRP, IL-6, and TNF-alpha levels — suggesting that part of TRT’s clinical benefit operates through anti-inflammatory mechanisms, not only through direct androgenic effects on muscle, bone, libido, and mood.
Autoimmune Disease and Testosterone
Men develop autoimmune diseases — rheumatoid arthritis, lupus, multiple sclerosis, thyroiditis, inflammatory bowel disease — at substantially lower rates than women. The sex ratio for many autoimmune conditions is 3:1 or greater in favour of female predominance. Testosterone’s immunosuppressive and Treg-promoting effects are a significant biological contributor to this sex difference.
Clinical observation supports this: autoimmune conditions in men often worsen during periods of testosterone decline (mid-life, post-illness, post-high-stress periods) and in some cases respond partially to testosterone restoration. Men with established autoimmune conditions and confirmed testosterone deficiency may find that TRT contributes to inflammatory control — though this is not a substitute for primary immunological treatment and should be discussed with the specialist managing the autoimmune condition.
COVID-19 and Testosterone: A Specific Recent Example
The COVID-19 pandemic provided a natural experiment in sex-based immune differences. Men consistently had worse COVID-19 outcomes than women — higher hospitalisation rates, higher ICU admission rates, and higher mortality. While multiple factors contribute (smoking, comorbidities, healthcare-seeking behaviour), the testosterone-immune relationship is among the proposed biological mechanisms. Some studies found lower pre-illness testosterone in men who had worse COVID outcomes, and others found that testosterone declined significantly during acute COVID illness.
Post-COVID fatigue syndrome (long COVID) frequently presents with symptoms overlapping significantly with testosterone deficiency — profound fatigue, cognitive difficulties, low mood, reduced exercise tolerance, and sexual dysfunction. At Vitalis Luxe Clinic, we have assessed men with post-COVID fatigue and found a meaningful proportion with co-existing testosterone deficiency — whether pre-existing and undiagnosed, or triggered by the acute illness and its systemic effects.
Frequently Asked Questions
Does low testosterone weaken the immune system?
Low testosterone is associated with elevated pro-inflammatory cytokines, reduced immune regulatory (Treg) cell function, and altered innate immune cell activity. The net clinical effect is not a simple ‘weaker’ immune system — rather, testosterone deficiency tends to shift immune function toward a pro-inflammatory, less well-regulated state. This is associated with higher rates of chronic inflammatory disease, poorer metabolic health, and potentially impaired immune surveillance, rather than simple increased susceptibility to all infections.
Does TRT affect the immune system?
TRT in hypogonadal men restores testosterone’s immunomodulatory effects — reducing pro-inflammatory cytokines (CRP, IL-6, TNF-alpha), supporting T regulatory cell function, and shifting macrophage polarisation toward the anti-inflammatory M2 phenotype. The clinical significance is most apparent in hypogonadal men with established chronic inflammatory disease — where TRT may contribute to inflammatory control alongside primary disease management.
Can testosterone help with autoimmune disease?
Testosterone’s anti-inflammatory and immunosuppressive properties suggest a potential role in autoimmune disease management in hypogonadal men. Clinical evidence is more observational than from large RCTs, but men with autoimmune conditions who have confirmed testosterone deficiency may experience partial improvement in inflammatory burden from TRT. This is a clinical discussion to have with both your TRT clinician and your immunology or rheumatology specialist — TRT does not replace primary immunological treatment but may complement it.
Why do men have lower rates of autoimmune disease than women?
Sex hormones are a major contributor to this difference. Testosterone’s immunosuppressive and T regulatory cell-promoting effects dampen the immune reactivity that drives autoimmune conditions. Oestrogen, conversely, promotes immune responsiveness — which contributes to female predominance in most autoimmune conditions. The testosterone-oestrogen balance is the primary hormonal mechanism underlying the consistent 3:1 or greater female-to-male ratio in most autoimmune diseases.
Can low testosterone cause inflammation?
Yes — testosterone deficiency is associated with chronic low-grade systemic inflammation: elevated CRP, IL-6, TNF-alpha, and other pro-inflammatory markers. This inflammatory state is not simply a consequence of other aspects of low testosterone — it is a direct consequence of lost testosterone’s immunomodulatory and anti-inflammatory effects. Chronic inflammation in turn drives many of the chronic disease risks associated with testosterone deficiency, including cardiovascular disease, metabolic syndrome, and osteoporosis.
Did COVID cause my low testosterone?
Acute illness generally suppresses testosterone transiently through inflammatory cytokine-mediated HPG axis suppression — COVID-19 is no exception. Whether this suppression persists as a chronic change depends on the severity of illness, the duration of immune activation, and pre-existing hormonal status. Men who have persistent fatigue, low mood, and sexual dysfunction after COVID warrant testosterone assessment alongside other post-COVID investigations. Testosterone deficiency may be pre-existing and undiagnosed, or genuinely triggered by the acute illness in some cases.
Where can I get a full hormonal assessment including immune markers in Hull or Yorkshire?
Vitalis Luxe Clinic in Hull provides comprehensive hormone assessment including testosterone, thyroid function, and inflammatory markers (CRP) for men with unexplained fatigue and post-illness symptoms across Hull, East Yorkshire, and throughout Yorkshire. Book your confidential consultation to discuss your full clinical picture.