Background
Proteins | Functions |
---|---|
Ionized calcium-binding adaptor molecule (Iba)1 | Cytoplasmic protein constitutively expressed by microglia, upregulated in inflammation. Iba1 is involved in cytoskeletal reorganization, membrane ruffling of the microglial processes and actin cross-linking needed for cell migration [23], thus reflecting microglial motility and migration properties. |
CD68 | CD68 labels lysosomal and endosomal transmembrane glycoprotein of microglia, indicating phagocytic activity [33]. |
Human leukocyte antigen (HLA)-DR | HLA-DR is a Major Histocompatibility Class (MHC) II cell surface receptor which presents antigens to cells of the immune system eliciting an immune response, involved in the non-self recognition and upregulated in inflammation [34]. |
Macrophage scavenger receptor (MSR)-A | MSR-A is a lipoprotein receptor involved in direct ligand recognition and scavenging activity. Its mouse homolog, scavenger receptor A (SR-A), is associated with plaques and release of reactive oxygen species and neurotoxic substances by microglia upon stimulation with fibrillar Aβ [35]. We previously showed a clustering pattern of MSR-A-positive microglia round plaques in Alzheimer's disease [16] suggesting expression of MSR-A may cause immobilization of the microglia when they encounter plaques [16, 26]. |
CD64 (Fcγ receptor I) | CD64 is a cell surface receptor with high affinity for the Fc portion of immunoglobulin (IgG), triggering a monocyte/macrophage response [30]. Expression of CD64 reflects the presence of immunoglobulins in the brain and thus the involvement of systemic immunity [36]. Overall FcγRs are important for antibody-dependent cytotoxicity, antigen presentation via MHC, clearance of antibodies and phagocytosis [37]. |
Methods
The CFAS cohort
Assessment of Alzheimer’s pathology
Immunohistochemistry
Microglial protein | Species | Clone/company | Dilution | Antigen retrieval technique |
---|---|---|---|---|
Iba1 | Rabbit | Polyclonal/Wako | 1:750 | Pressure cooker citrate pH 6 |
CD68 | Mouse | PG-M1/Dako | 1:50 | Microwave citrate pH 6 |
HLA-DR | Mouse | CR3/43/ThermoFisher Scientific | 1:200 | Microwave citrate pH 6 |
MSR-A | Goat | Polyclonal/R&D Systems | 1:500 | Microwave citrate pH 6 |
CD64 | Goat | Polyclonal/R&D Systems | 1:100 | Microwave EDTA pH 8 |
Quantification
Statistical analysis
Results
Characteristics of the cohort regarding dementia status
No dementia | Dementia with AD pathology | Dementia non-AD pathology | Unknown dementia status | |
---|---|---|---|---|
(n = 130) | (n = 83) | (n = 65) | (n = 21) | |
Number of womena
| 66 (51) | 53 (64) | 49 (75) | 10 (48) |
Age at death (years)b
| 84 (77; 90) | 89 (83; 93) | 89 (85; 93) | 86 (84; 91) |
Education (years)b
| 9 (9; 10) | 9 (9; 10) | 9 (9; 9) | 9 (9; 9) |
Years since last cognitive assessmentb
| 1.1 (0.5; 1.8) | 1.5 (0.8; 3.2) | 1.7 (0.8; 3.0) | 2.5 (2.0; 3.4) |
MMSE at last assessmentb
| 25 (22; 28) | 11 (6; 17) | 18 (11; 23) | 25 (22; 27) |
Iba1 load (%)c
| 2.346 (0.027) | 2.047 (0.027) | 1.824 (0.031) | 2.372 (0.070) |
CD68 load (%)c
| 0.090 (0.001) | 0.100 (0.002) | 0.088 (0.002) | 0.054 (0.002) |
HLA-DR load (%)c
| 0.213 (0.008) | 0.277 (0.011) | 0.143 (0.005) | 0.101 (0.007) |
MSR-A load (%)c
| 0.181 (0.003) | 0.188 (0.003) | 0.172 (0.003) | 0.171 (0.005) |
CD64 load (%)c
| 0.517 (0.006) | 0.523 (0.007) | 0.448 (0.007) | 0.523 (0.013) |
Microglia and cognition
Microglia (load (%)) | OR | 95 % CI (OR) |
P
|
---|---|---|---|
Iba1 |
0.86
| (0.82; 0.89) | <0.001
|
CD68 |
3.55
| (1.93; 6.51) | <0.001
|
HLA-DR | 1.06 | (0.96; 1.18) | 0.250 |
MSR-A |
1.56
| (1.11; 2.19) |
0.010
|
CD64 |
1.21
| (1.05; 1.39) |
0.007
|
Microglia (load (%)) | No dementia | Dementia with Alzheimer’s pathology | ||||
---|---|---|---|---|---|---|
β
| 95 % CI (β) |
P
|
β
| 95 % CI (β) |
P
| |
Iba1 |
0.37
| (0.29; 0.45) | <0.001
| −0.13 | (−0.32; 0.05) | 0.154 |
CD68 | −1.54
| (−2.96;−0.13) |
0.033
| −12.17
| (−15.13; −9.21) | <0.001
|
HLA-DR | 0.18 | (−0.04; 0.41) | 0.116 | −1.11
| (−1.59; −0.64) | <0.001
|
MSR-A | −0.69 | (−1.38; 0.00) | 0.051 | −4.94
| (−6.82; −3.07) | <0.001
|
CD64 | 0.27 | (−0.03; 0.58) | 0.076 |
1.08
| (0.15; 2.02) |
0.023
|
Microglia and Alzheimer’s neuropathology
Microglia (load (%)) | Meningeal CAA | Parenchymal CAA | Diffuse plaques | Neuritic plaques | Tangles |
---|---|---|---|---|---|
A. No dementia | |||||
Iba1 | 0.92 (0.84; 1.01) |
0.72 (0.65; 0.79) |
1.2 (1.15; 1.25) |
1.07 (1.02; 1.13) |
0.74 (0.68; 0.80) |
0.064 | <0.001
| <0.001
|
0.003
| <0.001
| |
CD68 |
0.09 (0.01; 0.99) |
0.00 (0.00; 0.01) |
8.62 (3.83; 19.40) |
0.02 (0.01; 0.07) | 1.07 (0.06; 19.41) |
0.049
| <0.001
| <0.001
| <0.001
| 0.965 | |
HLA-DR |
0.27 (0.16; 0.47) | 0.79 (0.56; 1.12) |
2.24 (1.77; 2.83) | 1.02 (0.91; 1.15) |
0.07 (0.02; 0.25) |
<0.001
| 0.183 | <0.001
| 0.728 | <0.001
| |
MSR-A |
0.16 (0.05; 0.47) |
0.03 (0.00; 0.35) | 1.42 (0.95; 2.13) |
0.24 (0.14; 0.40) | 0.44 (0.10; 1.96) |
0.001
|
0.005
| 0.09 | <0.001
| 0.283 | |
CD64 | 1.14 (0.77; 1.69) |
0.70 (0.52; 0.94) |
1.86 (1.57; 2.20) |
0.70 (0.58; 0.86) | 0.77 (0.45; 1.32) |
0.505 |
0.018
| <0.001
|
0.001
| 0.343 | |
B. Dementia with Alzheimer’s pathology | |||||
Iba1 |
1.36 (1.28; 1.45) |
1.53 (1.43; 1.64) |
1.37 (1.24; 1.51) |
1.5 (1.40; 1.61) |
1.14 (1.07; 1.21) |
<0.001
| <0.001
| <0.001
| <0.001
| <0.001
| |
CD68 | 1.07 (0.42; 2.73) | 1.40 (0.43; 4.55) |
0.17 (0.06; 0.48) |
31.65 (11.54; 86.81) |
49.28 (19.43; 124.99) |
0.892 | 0.576 |
0.001
| <0.001
| <0.001
| |
HLA-DR |
0.62 (0.52; 0.74) | 1.07 (0.94; 1.22) |
3.22 (2.50; 4.15) |
2.28 (1.65; 3.14) |
1.74 (1.42; 2.13) |
<0.001
| 0.302 | <0.001
| <0.001
| <0.001
| |
MSR-A |
2.43 (1.26; 4.66) |
2.24 (1.03; 4.84) |
2.44 (1.15; 5.21) |
10.31 (5.03; 21.11) |
3.24 (1.74; 6.04) |
0.008
|
0.041
|
0.021
| <0.001
| <0.001
| |
CD64 |
2.15 (1.71; 2.71) |
2.14 (1.63; 2.80) |
21.59 (14.22; 32.78) |
4.39 (3.39; 5.70) | 1.27 (0.99; 1.62) |
<0.001
| <0.001
| <0.001
| <0.001
| 0.056 |
Alzheimer’s pathology | No dementia | Dementia with Alzheimer’s pathology | ||||
---|---|---|---|---|---|---|
β
| 95 % CI (β) |
P
|
β
| 95 % CI (β) |
P
| |
Meningeal CAA | 0.48 | (−2.87; 3.82) | 0.779 | 0.49 | (−3.25; 4.24) | 0.794 |
Parenchymal CAA | −3.63 | (−9.33; 2.07) | 0.210 | 1.67 | (−3.04; 6.39) | 0.482 |
Diffuse plaques | 0.74 | (−0.67; 2.15) | 0.299 | 0.50 | (−3.45; 4.45) | 0.800 |
Neuritic plaques | 0.24 | (−1.61; 2.09) | 0.797 | −2.43 | (−5.84; 0.99) | 0.161 |
Tangles | 1.83 | (−3.90; 7.56) | 0.528 | −4.12
| (−7.60; −0.65) |
0.021
|
Microglia and APOE genotype
Microglia (load (%)) |
β
| 95 % CI (β) |
P
|
---|---|---|---|
ε2 | |||
Iba1 |
0.156
| (0.068; 0.244) |
0.001
|
CD68 | −0.010
| (−0.014; −0.005) | <0.001
|
HLA-DR | −0.036
| (−0.055; −0.017) | <0.001
|
MSR-A |
0.017
| (0.008; 0.026) | <0.001
|
CD64 | 0.020 | (−0.001; 0.040) | 0.060 |
ε4 | |||
Iba1 | −0.166
| (−0.237; −0.096) | <0.001
|
CD68 |
0.015
| (0.011; 0.019) | <0.001
|
HLA-DR |
0.042
| (0.019; 0.065) | <0.001
|
MSR-A | −0.004 | (−0.010; 0.003) | 0.317 |
CD64 |
0.041
| (0.024; 0.058) | <0.001
|