Table 2:

TSPO results in major depressive disorder by study

	Diagnosis (n)*		Treatment status	Brain region	Main result
	Major depressive disorder	Healthy controls
Hannestad et al (2013)30	9	10	8 unmedicated, 1 medicated	Frontal cortex; eight grey matter regions; centrum semiovale	Not significant
Setiawan et al (2015)31	20	20	All medication-free	PFC; ACC; insula; 14 grey matter regions	26–32% elevated during MDE
Setiawan et al (2018)32	50 (30 new†)	30 (10 new†)	30 medicated, treatment-resistant; 20 medication-free	PFC; ACC; insula; 14 grey matter regions	About 15–23% elevated during MDE; about 29–42% elevated in untreated major depressive disorder for more than 10 years
Richards et al (2018)27	28	20	12 medication-free; 16 medicated	sgPFC; ACC	About 25% elevated in sgPFC; about 15% elevated in ACC
Holmes et al (2018)33	14	13	No antidepressant or anti-inflammatory medications	PFC; ACC; insula	67% elevated in ACC; 28% elevated in PFC‡; 24% elevated in insula‡
Li et al (2018)34	40	20	Medication-naive	Frontal cortex; temporal cortex; hippocampus; whole grey and white matter	About 25–35% elevated during MDE
Li et al (2018)35	50 (10 new†)	30 (10 new†)	Medication-naive	Frontotemporal cortex; hippocampus; grey and white matter	About 25% elevated during MDE

All studies with quantitative results, statistical analyses, and that specified medication status of the participants were included. All studies used a second-generation radiotracer (either [¹⁸F]FEPPA or [¹¹C]PBR28) except the study by Holmes and colleagues,³³ which used [¹¹C]-(R)-PK11195. ACC=anterior cingulate cortex. MDE=major depressive episode. PFC=prefrontal cortex. sgPFC=subgenual prefrontal cortex. TSPO=18 kDa translocator protein.

^*All participants with major depressive disorder were studied during an MDE except for the study by Hannestad and colleagues,³⁰ in which four of nine participants were experiencing an MDE.

^†New participants not included in other studies listed in this table.

^‡Results were not statistically significant.