Possible solution off https://stackoverflow.com/questions/46406022/how-to-connect-a-signal-to-a-slot-in-a-different-thread

main.py

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        self.keyworddict = {}
        self.count = {}
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(698, 581)
        MainWindow.setMinimumSize(QtCore.QSize(698, 581))
        MainWindow.setMaximumSize(QtCore.QSize(698, 581))
        palette = QtGui.QPalette()
        brush = QtGui.QBrush(QtGui.QColor(154, 161, 161))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Active, QtGui.QPalette.Button, brush)
        brush = QtGui.QBrush(QtGui.QColor(206, 206, 206))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Active, QtGui.QPalette.Base, brush)
        brush = QtGui.QBrush(QtGui.QColor(214, 214, 214))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Active, QtGui.QPalette.Window, brush)
        brush = QtGui.QBrush(QtGui.QColor(154, 161, 161))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Inactive, QtGui.QPalette.Button, brush)
        brush = QtGui.QBrush(QtGui.QColor(206, 206, 206))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Inactive, QtGui.QPalette.Base, brush)
        brush = QtGui.QBrush(QtGui.QColor(214, 214, 214))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Inactive, QtGui.QPalette.Window, brush)
        brush = QtGui.QBrush(QtGui.QColor(154, 161, 161))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Disabled, QtGui.QPalette.Button, brush)
        brush = QtGui.QBrush(QtGui.QColor(214, 214, 214))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Disabled, QtGui.QPalette.Base, brush)
        brush = QtGui.QBrush(QtGui.QColor(214, 214, 214))
        brush.setStyle(QtCore.Qt.SolidPattern)
        palette.setBrush(QtGui.QPalette.Disabled, QtGui.QPalette.Window, brush)
        MainWindow.setPalette(palette)
        self.centralWidget = QtWidgets.QWidget(MainWindow)
        self.centralWidget.setObjectName("centralWidget")
        self.comboBox = QtWidgets.QComboBox(self.centralWidget)
        self.comboBox.setGeometry(QtCore.QRect(20, 60, 371, 31))
        font = QtGui.QFont()
        font.setFamily("Yu Gothic")
        font.setPointSize(16)
        self.comboBox.setFont(font)
        self.comboBox.setAcceptDrops(False)
        self.comboBox.setObjectName("comboBox")
        self.comboBox.addItem("")
        self.comboBox.addItem("")
        MainWindow.setCentralWidget(self.centralWidget)
        self.retranslateUi(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.comboBox.setItemText(0, _translate("MainWindow", "Jackets"))
        self.comboBox.setItemText(1, _translate("MainWindow", "Shirts"))


class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        QtWidgets.QMainWindow.__init__(self, parent)
        self.setupUi(self)

        self.thread = Threadclass2(self)
        self.comboBox.currentTextChanged.connect(self.thread.setText)
        self.thread.start()


class Threadclass2(QtCore.QThread):
    def __init__(self, parent=None):
        super(Threadclass2, self).__init__(parent)
        self._text = ""
    
    def setText(self, text):
        self._text = text

    def run(self):
        while True:
            print(self._text)
            QtCore.QThread.sleep(0.1)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())