A Review Article On Host-Directed Therapies In Tuberculosis And Sepsis: Overcoming Antimicrobial Resistance Through Immune Modulation

Illnesses often start small - invisible threats such as bacteria, viruses, fungi, or parasites slipping into the body unnoticed¹⁰. Inside, they grow quietly, disrupting normal operations, possibly damaging parts of us we rely on. Our immune system tackles many without help, but a few slip past its guard, demanding medical care to prevent worse outcomes^11,12. Gains made by science - shots that protect, pills that kill, actions that warn communities - have saved countless lives over time. Even so, fresh dangers keep emerging, while old remedies fade in strength, threatening what we’ve built.

Back and forth they evolve, hosts and bugs caught in a constant tug of life. A mild bug might flare into crisis when the immune system drags its feet¹³. Lacking proper food or managing diseases such as diabetes gives invaders room to grow¹⁴. Cancer - or drugs that dull the body’s guard - lets germs settle deeper inside¹⁵. Common battles too - breathing problems over years or using substances without care - tip balance toward harm.

One way to fight infection skips going after germs entirely. Host cells become the focus, guided by treatments shaping their inner environment. Rather than hitting microbes head-on, certain drugs tune how the body responds. Immune signals get adjusted, inflammation gets checked, and cell behavior shifts subtly. Medicines once meant for other illnesses help reshape these internal conditions. Survival tools used by invaders may lose their edge when the host changes. Defenses rise without pushing pathogens into resistant forms¹⁶. Balance returns where chaos once ruled during sickness. Traditional drugs kill bacteria directly - this path strengthens human resilience instead. Pressure to evolve fades since the treatment does not chase bacterial parts. Broad reach emerges simply because the strategy avoids targeting one microbe type. Resistance risks shrink as a result of this indirect route. When sickness hits hard - think sepsis or TB - it's not just germs causing trouble. The body’s own immune confusion often makes things worse. That’s where HDTs step in. Not by killing bacteria directly, but by calming chaotic inflammation. These treatments target how the host reacts, not only has what infected them. Heavy microbial load matters, yes. Yet out-of-control immune behavior can be just as dangerous. So fixing response patterns becomes key. Instead of adding more stress on an overwhelmed system, support its balance. Research shows this shift in focus helps stabilize critical conditions. Healing isn’t always about attack. Sometimes it’s about guidance.

Battles between bacteria and bodies come down to timing, strength, and shift. One side pushes, the other resists - neither always wins. Macrophages wake up, swallow invaders, recycle parts; inside cells, cleanup crews sort waste, trap threats¹⁷. Signals spread, calling specialized units like T cells, B cells - they learn, adapt, remember faces. But when hunger skews body chemistry, or vitamins run low, armor thins. Diabetes drags response times. HIV empties defense ranks. Medicine meant to calm overactive systems sometimes opens back doors. Poverty shapes risk just as much as genes do¹⁸. Fixing broken signals in human tissue - not only attacking bugs directly - offers a slower burn against drug-resistant strains.

These days, superbugs outsmart medicine faster than ever. Soon as penicillin showed up, troublemakers learned how to dodge it - leading straight into a surge of stubborn infections forcing clinics to reach for last-resort pills such as carbapenems or colistin ¹⁹. Facing roadblocks at every turn, scientists shift focus - not killing bugs but boosting what the body already uses to defend itself ²⁰.

Tuberculosis and Sepsis: Pathogenesis and Antimicrobial Resistance

Germs called Mycobacterium tuberculosis lead to tuberculosis, marked by clumps forming in tissues - a sign the body tries to wall off infection²¹. When these clumps stay firm, they often keep bacteria in check; if they turn soft and dead-like, damage spreads instead²² .Usual care involves multiple drugs taken nonstop for half a year or more, yet rising strains that resist key medicines now challenge recovery paths. Some germs dodge both isoniazid and rifampicin - two mainstays of therapy - making healing harder.

Some TB strains resist even more medicines than usual. These do not respond to certain antibiotics that normally work after first ones fail. When germs ignore both early treatments and later options like injections or specific pills, doctors call it XDR-TB. It happens when bacteria survive drugs meant to stop them in tougher cases when the body fights an infection, sometimes it overreacts - that can lead to sepsis, a serious condition tied to many types of germs like Gram-positive, Gram-negative, and fungi²³. Molecules from microbes, known as PAMPs, along with signals released by injured cells called DAMPs, switch on immune reactions²⁴ - these spark swelling across tissues and harm organs. Now more than ever, treating sepsis gets harder because some bugs resist drugs, especially those with multiple defenses such as ESBL-making bacteria or VRE²⁵.Host-Directed Therapies in Tuberculosis

Immunopathogenesis and Macrophage Dysfunction

Inside the body, Mtb mainly lives in macrophages, yet dendritic cells along with neutrophils play roles in how illness develops. Rather than let defenses work, Mtb blocks merging of phagosomes and lysosomes, hinders self-cleaning processes, slips into cell fluid, while also encouraging fat buildup inside infected macrophages²⁶. Because of these shifts caused by bacteria, removal fails, survival becomes easier. Helping immunity regain balance - this is what HDTs target - with focus on reviving worn-out responses and strengthening frontline cell actions against invaders²⁷.

Vitamins as Host-Directed Therapies

A few research projects suggest vitamin D speeds recovery in those with tuberculosis. Since it plays a role in how the body defends itself, scientists pay close attention to its effects. Not simply revving up defenses, it sets off specific reactions designed to attack invaders. One way is by raising levels of destructive particles such as ROS within infected cells. Meanwhile, it activates a built-in compound known as cathelicidin, which destroys pathogens. It also helps clear out damaged cells, making it easier for the body to handle infections. Still, not all studies agree on how well it works. Some noticed people got better faster when looking at cough outcomes and signs of illness. Yet a few found almost no difference at all. People respond in their own way, which could be why findings are so mixed. Figuring out the best amount to use hasn’t been straightforward either.

Vitamin A, along with related compounds like all-trans retinoic acid, slows Mtb expansion by triggering acid buildup inside phagosomes while adjusting immune reactions. Even though lab tests show promise, giving extra vitamin A hasn’t always led to better results in patients - hinting that picking the right people and amounts matters a lot.

Cytokine-Based Host-Directed Therapies

Macrophages wake up when signals like TNF, IFN-γ, or IL-1 show up - each plays a distinct role inside the body's defense hubs. Instead of working together, these molecules take separate paths: one speeds up trash removal in cellular pockets, another fuels reactive oxygen strikes, while the third boosts small protein fighters and quiets down harmful immune echoes. Granulomas hold their shape because of this quiet coordination happening behind the scenes. Each signal arrives at different moments, yet fits into the larger pattern without overlap.

Too much cytokine activity might worsen harm to tissues and make illnesses more severe. In studies where people breathed in IFN-γ, mucus cleared faster yet lung scans showed mixed results - proof that treatments targeting cytokines walk a fine line between help and harm ²⁸.

Pharmacological Induction of Autophagy

Inside cells, autophagy helps block Mtb by cleaning out invaders. Metformin kicks off this process, making it harder for bacteria to survive. Statins join in, turning up cellular cleanup routines naturally. Tyrosine kinase inhibitors nudge the system further, adding pressure on pathogens. Anticonvulsants chip away at barriers that protect Mtb inside cells. Selective serotonin reuptake inhibitors also pitch in, boosting internal defenses quietly. Each of these already-approved medicines shifts autophagy into higher gear.

Metformin shows real promise because it turns on a key enzyme called AMPK. This shift helps clean up cellular debris more efficiently through better phagosome development. Energy shifts inside cells lead to higher mitochondrial ROS levels, which play a role in controlling infection. In lab tests, these changes result in fewer bacteria surviving. Statins add another layer by blocking harmful fat buildup in immune cells. They stop macrophages from turning into foamy versions that shelter germs. Evidence from broad population reviews reveals no spike in TB flare-ups among statin users. That pattern makes them strong candidates for added treatment roles.

Immune Checkpoint Modulation

Tired immune responses pop up during long-lasting TB infections, where cells carry more stop signs such as PD-1, CTLA-4, LAG-3, and TIM-3^29,30. Blocking these brakes wakes up T-cells, increases IFN-γ, while helping macrophages clear out MT - seen only in controlled studies so far³¹. Yet pushing the immune system too hard might harm lung tissue, making checkpoint drugs tricky to apply safely in real-world TB cases.

Hidden within an immune cell, therapies target the way the body reacts rather than striking pathogens outright. After entering, the TB bacterium escapes breakdown by halting fusion between its capsule and waste-processing zones. Illustrated here is how these methods reawaken trapped defenses. Their survival stretches on since the invader suspends its degradation internally. Action comes through shifting cellular habits, never through direct microbial elimination. When normal cleanup processes get disrupted, germs stick around longer once they invade. Healing shows up not through drugs that kill bacteria, but by shifting how the body's own systems respond^31,32.

 Metformin, along with certain tyrosine kinase blockers and statins pictured here, helps restart stalled phagosome development. These compounds push through to full lysosomal merging. That shift creates an aggressive autophagolysosome environment inside cells. The result? Mycobacterium tuberculosis faces stronger internal destruction. Proof sits in studies six, seven, thirty-eight, and thirty-nine.

Inside cells, a cleanup process helps fight TB bacteria when turned on by certain substances. Vitamin D kicks it off, just like diabetes medicine metformin does. Blocking mTOR has a similar effect. Some cancer drugs, including gefitinib, play a role too³³. Cholesterol treatments known as statins are part of this mix. Blood pressure pills such as verapamil also contribute. Even antidepressants like fluoxetine get involved. An antiparasitic drug, nitazoxanide, shows up here. Seizure medications - carbamazepine and valproic acid - are included as well. These helpers clear out harmful microbes hiding inside. They slow down how fast the germs multiply.

Immune activity shown here relies on signaling molecules like interferon-γ, tumor necrosis factor, and interleukin-1. Because of these, macrophages boost their ability to destroy microbes. Phagosomes change more quickly into killing compartments when triggered this way. Reactive oxygen builds up thanks to such signals lighting up cellular pathways. Autophagy gets switched on, too, helping clear out invaders. Treatment using interferon-γ might push this response further. Modulating TNF could tilt the balance toward stronger defense. PDE inhibitors also play a role in lifting these reactions. Yet if cytokine actions grow too strong, damage to tissues often follows.

What stands out is how vitamin D, along with HDAC inhibitors and phenyl butyrate, ramps up antimicrobial peptides like cathelicidin - this boosts macrophages’ ability to destroy pathogens^34-36. Starting from another angle, statins and vitamin D block lipid bodies, which cuts off resources for Mtb while stopping foamy macrophage development that lets bacteria survive³⁷.

Sepsis

Epidemiology Meets Immune System Challenges

Most years, across the globe, sepsis takes a heavy toll - the immune system overreacts to an infection, harming vital tissues. While medical care has advanced, far too often, lives are lost anyway³⁸.

One person’s body fights sepsis differently than the next - patterns shift without warning. Not step-by-step, but side by side: firestorms of swelling share space with a drained defense system. From the start, alarm systems spark chemical flares, lighting up pathways that race through the blood.

Later on, the body starts losing key infection-fighting cells through programmed death. The ability to generate protective chemicals drops off sharply. Immune markers like HLA-DR fade away. At the same time, receptors that dampen defense responses grow more common. As these shifts take hold, germs linger longer. New infections gain ground more easily.

Antimicrobial Use and Resistance in Sepsis

Speed changes everything when antibiotics hit sepsis - waiting can tip survival one way or another. Not every microbe listens anymore, particularly stubborn Gram-negative strains and vancomycin-defying enterococci flooding clinics lately. When answers hide, physicians grab broad-spectrum tools, yes, but that choice occasionally arms the enemy instead of stopping it.

Barriers to Host-Directed Therapy Development in Sepsis

Most treatments aimed at the body's response - like those blocking TNF-α or IL-1, targeting TLR4, using IV immunoglobulin, or activated protein C - didn’t work out in big trials⁵¹. Problems came up because patients weren’t grouped well, conditions were too broadly defined, plus researchers didn’t fully grasp how varied immune responses can be observed ⁴⁰.

Right now, how we define sepsis leans mostly on visible symptoms, skipping details about a person’s immunity or how far the illness has progressed. Because of this, groups of patients end up mixed in unclear ways, making treatments seem less effective than they might be appear ⁴¹