New Study Reveals Surprising Distribution of Human Immune Cells


A recent study conducted by researchers in Israel has provided a quantitative mapping of the distribution, abundance, and mass of primary immune cells across various human tissues. The study, published in the journal PNAS, utilized integrated biotechnological methods to gain a deeper understanding of the immune system’s cellular network.

Understanding the Distribution of Immune Cells

The distribution of immune cells within the human body is crucial for maintaining overall health. However, due to the cellular diversity and limitations of previous studies, understanding this distribution has remained challenging. Existing research has often been focused on specific areas and methodologies, lacking comprehensive data specific to humans. This has led to debates regarding the most immunogenic organ. Therefore, further research is needed to clarify the distribution of immune cells, reconcile discrepancies in previous studies, and enhance our understanding of immune functionality in humans.

Mapping the Human Immune System

The recent study aimed to comprehensively map the human immune system by categorizing cells into lymphoid and myeloid groups. The researchers used a healthy young male as a reference to establish baseline cell densities. The study utilized three methodologies: an extensive literature review, high-resolution multiplexed imaging, and a novel methylation-based deconvolution technique. The literature review updated historical data to provide modern estimates of cell density, taking into account tissue characteristics and utilizing advanced techniques such as flow cytometry for relative abundance data. Tissues and organs were categorized based on anticipated immune cell presence, providing a systematic structure for analysis.

Detailed Findings on Immune Cell Density and Distribution

The study revealed detailed insights into the density and distribution of immune cells across human tissues. The data, obtained from a meticulous literature survey, provided information about the density of different cell types in tissues with similar compositions and functions. The lymphatic system and bone marrow exhibited the highest densities of immune cells due to their primary composition of these cells. In contrast, epithelial organs had significantly lower densities.

Specific immune cells displayed distinct distribution patterns. Macrophages, T cells, and B cells were found to vary greatly across tissues, while plasma cells and eosinophils were primarily located in the gastrointestinal tract. Interestingly, adipose and skeletal muscle tissues, which account for approximately 75% of the body’s cellular mass, contained only 0.2% of the total immune cell count. This can be attributed to the larger size of cells in these tissues.

The study also estimated the total count of immune cells in various tissues, approximating it to be around 1.8 × 1012 using a standard human model that combined tissue-specific immune cell densities with organ mass. Most immune cells were found in the bone marrow and lymphatic system, with diverse cell types dispersed in different ratios across each organ system.

Further analysis revealed a heterogeneous makeup of immune cells within tissues. Neutrophils were found to dominate the bone marrow, while lymphocytes were more prevalent in the lymphatic system. Mast cells and macrophages were prominent in tissues such as the gastrointestinal tract, skin, and lungs.

The study validated the estimates using a methylation atlas-based deconvolution approach, confirming the literature-based findings, particularly for lymphocytes. However, discrepancies were observed for granulocytes.

In addition to determining the distribution of immune cells, the study also estimated the mass of these cells. By aggregating data on cell sizes and volumes, the total immune cell mass in the body was approximated to be 1.2 kg. The distribution of mass varied from the distribution of cell count, primarily due to variations in cell sizes. Macrophages, due to their larger size, accounted for a significant portion of the total immune cell mass.

Implications of the Study

The study challenges the notion that the majority of immune cells reside in the gut and instead reveals that primary sites include the bone marrow, lymph nodes, and spleen. It sheds light on the role of the gut in antibody production and the immunological functions performed by the liver. The findings were validated through multiple analyses, ensuring their reliability. The study also took into account variations in immune cell distribution based on sex, age, and health status, indicating a standardized pattern throughout the human body.

Overall, the study provides new estimates on immune cell count, mass, and distribution in humans, highlighting the complexity of immune cell distribution and emphasizing the need for comprehensive data and advanced methodologies in future research.


  1. Source: Coherent Market Insights, Public sources, Desk research
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