This Immune Booster podcast episode, recorded at the 2024 Society for Leukocyte Biology meeting, features Dr. Holger Heine discussing his research journey into innate immunity, from early work on bacterial lipopolysaccharide (LPS) recognition to his more recent and groundbreaking investigations into how the immune system detects Archaea. Dr. Heine recounts the historical context of identifying TLR4 as the LPS receptor, including the initial confusion around TLR2. The core of the discussion centers on the discovery that Archaea, a largely overlooked domain of life in immunology, are primarily recognized by the innate immune system through their RNA via TLR8 following phagocytosis and lysosomal processing. He explores the implications of this, the current understanding of Archaea in health and disease (noting the absence of known archaeal pathogens to date), differences in immune signaling compared to bacteria, and the potential for Archaea-bacteria interactions to modulate immune responses.
Exploring Innate Immunity to Archaea with Dr. Holger Heine
0:29 Introduction to Dr. Holger Heine: Dr. Heine is the head of a research laboratory in innate immunity and deputy director of the program for chronic lung disease at the Research Center Borstel, Leibniz Lung Center in Germany.
1:32 Scientific Beginnings: Dr. Heine's interest in science began in school with biology and chemistry, leading him to study biology. Immunology lectures at the Research Center Borstel sparked his passion for the field.
2:40 Early Research on Microbial Compounds: During an internship in the early 90s, he investigated how synthetic microbial compounds, including various Lipopolysaccharide (LPS) structures, activated human immune cells, even before Toll-like Receptors (TLRs) were well understood.
5:06 LPS Receptor Discovery Era: His diploma and PhD work focused on how specific LPS structures were recognized by immune cells. He collaborated with a Japanese group (Shuichi Kuzumoto) that synthesized these structures.
7:07 Postdoctoral Work and TLRs: Dr. Heine did a postdoc at Boston University with Dr. Douglas Golenbock. He describes the exciting period of TLR discovery, including the initial, incorrect, identification of TLR2 as the LPS receptor. His lab found that CHO cells, highly sensitive to LPS, had a non-functional TLR2, suggesting TLR2 wasn't the primary LPS receptor, and that contamination of LPS with lipopeptides (TLR2 ligands) caused the confusion. TLR4 was later identified as the correct LPS receptor.
10:07 Pivoting to Archaea: Dr. Heine was approached by a colleague, Ruth Schmitz-Streit, leading him to investigate the immune recognition of Archaea, a domain of life often overlooked in microbiome studies, which historically focused on bacteria.
11:56 Immune Recognition of Archaea: His lab found that Archaea induce strong immune responses in human cells.
13:43 TLR8 Recognizes Archaeal RNA: The mechanism of Archaea recognition was found to be similar to certain "cowshed bacteria" they had studied. Archaea are taken up by immune cells, digested in phagolysosomes, and their RNA is then recognized by TLR8, signaling the presence of a live microbe.
16:17 Archaea and Pathogenicity: Dr. Heine discusses that, currently, there are no known human pathogens among Archaea, though some are associated with diseases like IBD and asthma. He believes pathogenic Archaea might still be discovered, especially among the many unculturable "dark impeta."
18:30 Signaling Differences: Archaea vs. Bacteria: Archaeal recognition, primarily via TLR8 and requiring uptake, leads to a distinct and somewhat delayed signaling cascade compared to bacteria, which activate multiple surface and internal receptors (e.g., TLR4, TLR2, NODs).
19:34 Diversity in Archaeal Immunogenicity: Not all Archaea are equally immunogenic. For instance, Methanobrevibacter smithii, common in the human gut, initially induces a weaker response, suggesting potential involvement of other receptors or uptake mechanisms.
20:20 Archaea-Bacteria Interactions: Archaea, like methanogens, play crucial roles in gut ecosystems (e.g., syntrophy, removing H+ from fermentation). Interactions between bacteria and Archaea can alter microbial structures and potentially modulate immune responses, an area ripe for further research.
21:45 Advice for Trainees: Dr. Heine advises young scientists to explore different topics, find what they are truly passionate about, and pursue it diligently, even if others doubt its initial importance.