**Good Cop, Bad Cop: The Opposing E**ff**ects of Macrophage Activation State on Maintaining or Damaging FunctionȱΆȬell Mass**

#### **Daelin M. Jensen, Kyle V. Hendricks, Austin T. Mason and Je**ff**ery S. Tessem \***

Nutrition, Dietetics and Food Science Department, Brigham Young University, Provo, UT 84602, USA; daelinmichael@gmail.com (D.M.J.); kylev.hendricks@gmail.com (K.V.H.); austintaylormason@gmail.com (A.T.M.)

**\*** Correspondence: Jeffery\_tessem@byu.edu

Received: 20 October 2020; Accepted: 24 November 2020; Published: 26 November 2020

**Abstract:** Loss of functional β-cell mass is a hallmark of Type 1 and Type 2 Diabetes. Macrophages play an integral role in the maintenance or destruction of pancreatic β-cells. The effect of the macrophage β-cell interaction is dependent on the activation state of the macrophage. Macrophages can be activated across a spectrum, from pro-inflammatory to anti-inflammatory and tissue remodeling. The factors secreted by these differentially activated macrophages and their effect on β-cells define the effect on functional β-cell mass. In this review, the spectrum of macrophage activation is discussed, as are the positive and negative effects on β-cell survival, expansion, and function as well as the defined factors released from macrophages that impinge on functional β-cell mass.

**Keywords:** β-cell; macrophage; islet; cytokine; diabetes
