diff --git a/Services.ZUGFeRDService/ThreadRunner.vb b/Services.ZUGFeRDService/ThreadRunner.vb
index 7bd310af..8a969115 100644
--- a/Services.ZUGFeRDService/ThreadRunner.vb
+++ b/Services.ZUGFeRDService/ThreadRunner.vb
@@ -14,18 +14,12 @@ Public Class ThreadRunner
     Private WithEvents _workerThread As BackgroundWorker
     Private WithEvents _workerTimer As Timer
 
-    Private _config As ConfigManager(Of Config)
-    Private _logConfig As LogConfig
-    Private _logger As Logger
-    Private _firebird As Firebird
-    Private _watchDirectories As List(Of String)
-    Private _successDirectory As String
-    Private _errorDirectory As String
-    Private _originalEmailDirectory As String
-    Private _attachmentDirectory As String
-    Private _zugferd As ZUGFeRDInterface
-    Private _jobArguments As WorkerArgs
-    Private _mssql As MSSQLServer
+    Private ReadOnly _config As ConfigManager(Of Config)
+    Private ReadOnly _logConfig As LogConfig
+    Private ReadOnly _logger As Logger
+    Private ReadOnly _firebird As Firebird
+    Private ReadOnly _jobArguments As WorkerArgs
+    Private ReadOnly _mssql As MSSQLServer
 
     Public Sub New(LogConfig As LogConfig, ConfigManager As ConfigManager(Of Config), Firebird As Firebird, Optional MSSQL As MSSQLServer = Nothing)
         _logConfig = LogConfig