Lipopolysaccharides (LPS) were first studied in the early 1900s, when scientists recognized that certain heat-stable components of Gram-negative bacteria could trigger fever and immune activation even after the bacteria were inactivated. Early researchers called these molecules “endotoxin,” and by the mid-20th century, LPS had become one of the most studied bacterial surface structures because of its ability to stimulate the immune system.
By the 1950s and 1960s, LPS was firmly established as the immune-activating component of the Gram-negative outer membrane. Its structure (Lipid A, core oligosaccharide, and O-antigen) was mapped, and its ability to provoke fever, shock, and inflammation is foundational to immunology and infectious disease research.
Why LPS Matters
LPS is increasingly recognized as a driver of chronic inflammatory disease, well beyond its role in sepsis. Even low-grade endotoxemia (sub-clinical amounts of LPS entering circulation) can sustain inflammation in ways that contribute to neurodegenerative, metabolic, and cardiovascular disease.
LPS activates the innate immune system through Toll-like receptor 4 (TLR4), triggering NF-κB signaling and cytokine release. This pathway is so fundamental that it shows up across multiple disciplines:
Cardiology: LPS exposure can induce inflammatory injury and electrical dysfunction in human cardiomyocytes.
Immunology: LPS is the gold-standard ligand for activating macrophages through TLR4. It’s routinely used to study cytokine release, inflammasome activation, antigen presentation, and innate immune priming. Much of what we know about NF-κB signaling, IL-1β maturation, and innate immune cascades comes from LPS-based models.
Gastroenterology: LPS combined with hypoxia reliably induces gut inflammation, epithelial apoptosis, and NEC-like intestinal injury in term and preterm rats. LPS is also implicated in adult GI disorders: elevated endotoxin levels are associated with increased intestinal permeability, visceral hypersensitivity, and symptom flares in IBS, underscoring its role in gut-immune interactions.
Chronic disease research: Persistent low-level LPS exposure (sometimes called metabolic endotoxemia) is linked to type 2 diabetes, atherosclerosis, non-alcoholic fatty liver disease, and inflammatory bowel disease. Even small increases in circulating LPS can sustain systemic inflammation, impair insulin signaling, and contribute to cardiometabolic dysfunction.
What is LPS Doing in Donor Human Milk?
If LPS is this biologically active at low levels, the next question is where infants encounter it, especially neonates with compromised immune systems.
A 2025 study of at-home pumping practices found that Gram-negative bacteria are a normal part of the human milk microbiota, and their presence varies with hygiene and pump-kit cleaning methods. Milk expressed with less-sterile equipment had higher total Gram-negative bacterial counts, including Proteobacteria, a major Gram-negative phylum.
A 2022 comparison of donor human milk (DHM) and preterm mothers’ own milk found that DHM had significantly higher proportions of Pseudomonas, a Gram-negative genus known for robust LPS structures. Pasteurization alters the microbiota but doesn’t eliminate Gram-negative bacterial fragments; in fact, DHM showed greater microbial diversity and persistent Gram-negative signatures even after heat treatment.
Holder pasteurization reliably inactivates Gram-negative organisms, but the LPS “shells” remain intact. This is a known property of endotoxin biology and is acknowledged in food-science and milk-processing literature.
A small number of studies have quantified endotoxin levels in human milk before and after pasteurization. These papers confirm that endotoxin persists, but most stop at measurement. None propose a method to reduce LPS exposure, and few evaluate clinical implications.
What are the clinical implications of LPS in neonates?
For preterm infants, whose intestinal barriers and immune systems are still developing, LPS can bind to receptors in the gut that trigger inflammation, and immature immune defenses amplify that response.
The premature intestine overexpresses TLR4 and responds abnormally to LPS. In preterm animals and human tissue, TLR4 expression is higher in the immature intestine than in the term intestine, and its activation by LPS leads to enterocyte apoptosis, impaired mucosal repair, and increased permeability. This exaggerated response is described as a central mechanism in NEC pathogenesis.
Experimental NEC models (mouse, rat) combine formula feeding, hypoxia, and LPS exposure to reliably produce NEC-like intestinal injury. When TLR4 is deleted or inhibited, LPS no longer induces the same degree of damage, which is taken as strong causal evidence.
The premature intestine reacts abnormally to small, sub-clinical LPS exposure. That early injury unfolds at the mucosal surface, and by the time NEC becomes clinically visible, the LPS-driven apoptosis, impaired repair, and barrier disruption have already occurred. The process that leads to NEC is largely invisible at the bedside, which is why the relevance of low-grade LPS exposure has been easy to miss in day-to-day neonatal practice.
Why the LPS Problem Has Been Invisible
Although the role of LPS in driving intestinal inflammation is well described in the literature, it hasn’t been a focus of clinical practice because there’s never been a practical way to reduce LPS exposure in DHM. Without a modifiable intervention, the risk has simply been treated as part of the landscape.
NEC mitigation currently focuses on the risks clinicians have some control over: using human milk over formula, cautious feeding advancement, infection control, antibiotic stewardship, and (in some countries) probiotics.
Milk-banking standards are built around bacterial safety; they eliminate live pathogens, but lack the technology to address fragments like LPS.
How the Bovine Milk Industry Solved a Similar Problem
In bovine milk processing, Gram-negative bacteria and their heat-stable fragments have been identified as contributors to quality degradation and inflammatory responses in calves. Heat alone doesn’t address these components.
To solve this, the dairy industry adopted bactofugation, a mechanical clarification step that uses centrifugal force to remove bacterial cells and cell-wall fragments before pasteurization. This approach complements heat treatment by targeting what heat can’t reach. Over time, bactofugation became a standard tool for improving microbial quality in bovine milk precisely because it reduced exposure to heat-stable bacterial debris.
Where Donor Human Milk Goes From Here
The bovine milk industry identified the problem, developed a mechanical solution, and made it standard practice. Donor human milk is at the same inflection point. The biology is well established, the gap in current processing is documented, and the clinical stakes, particularly for the most vulnerable preterm infants, are high.
LactaLogics is applying bactofugation to donor human milk. This is the first known application of this technology in human milk processing.