**2. Classification of macrophages by the tissue**

#### **2.1 Adipose tissue macrophages: Adipose tissue**

Macrophages exist in body fat and increase in case of obesity.

#### **2.2 Monocytes: bone marrow, blood**

The largest white blood cells in the blood. They develop into macrophages and dendritic cells.

#### **2.3 Kupffer cells: liver**

Kupffer cells exist in the liver and also known as stellate macrophages. Kupffer cells were named after Karl Wilhelm von Kupffer. They work as the first defence against gut bacteria and endotoxin in the liver.

#### **2.4 Alveolar macrophages: pulmonary alveoli**

Macrophages exist in alveoli and bronchus. Alveolar macrophages have high activity to get rid of dusts and microbes in the lung.

#### **2.5 Microglia: central nerve system**

A family of glial cells with different origin from other family of cells. Most of glial cells developed from ectoderm; however, alveolar macrophages are developed from mesoderm and haematopoietic stem cells. Microglia have phagocytic activity in the nerve and participate in the repair of neural tissue after the tissue damage.

#### **2.6 Hofbauer cells: placenta**

Eosinophilic histocytes found in the placenta, often seen in early pregnancy, named after J. Isfred Isidore Hofbauer. Hofbauer cells are considered as a type of macrophage.

#### **2.7 Intraglomerular mesangial cells: kidney**

Intraglomerular mesangial cells exist in basement membrane surrounded by glomerular capillaries. They are considered as a type of fibroblast.

#### **2.8 Osteoclasts: bone**

Osteoclasts are the specialist of absorbing or destroying bone in the process of bone regeneration. They are usually polygonal giant cells with 5–20 nuclei, but sometimes mononuclear osteoclast can be found. Bone marrow-derived monocyte progenitors differentiate into osteoclasts. The marker of osteoclasts is tartrate-resistant acid phosphatase. On the other hand, the marker of osteoblast is alkaline phosphatase.

#### **2.9 Langerhans cells: skin**

Langerhans cells are named after Paul Langerhans. Usually, they are regarded as dendritic cells other than macrophages.

#### **2.10 Epithelioid cells: granulomas**

Activated macrophages similar to epithelial cells. They have a thin eosinophilic cytoplasm with small granules and nucleus less dense than lymphocytes. They are found in granulomatous inflammation and participate in arthritis.

#### **2.11 Red pulp macrophages (sinusoidal lining cells): red pulp in spleen**

Macrophages found in red pulp in spleen are necessary for the blood homeostasis by depleting damaged or aged red blood cells with the phagocytosis.

#### **2.12 Intestinal macrophages: intestine**

Macrophages specifically evolved in intestinal environment. Intestinal macrophages do not induce inflammation to coexist with intestinal microbiome. They do not excrete proinflammatory cytokines such as IL-1, IL-6, and TNF-α. TGF-β produced by surrounding environment changes these macrophages from proinflammatory phenotype to non-inflammatory phenotype. Intestinal macrophages conduct phagocytosis, but they do not produce cytokines after phagocytosis nor express receptors for LPS, IgA, and IgG.

#### **2.13 Others**

Sinus histiocytes: lymph nodes Tissue macrophages leading to giant cells: connective tissue Peritoneal macrophages: peritoneal cavity LysoMac: Peyer's patch
