Light micrograph of bronchopneumonia, a form of pneumonia which causes inflammation of the bronchi, and spreads out to inflame the alveoli. In bacterial pneumonia, invasion of the lung parenchyma by bacteria produces an inflammatory immune response. This response leads to a filling of the alveolar sacs with exudate. The loss of air space and its replacement with fluid is called consolidation. In bronchopneumonia, or lobular pneumonia, there are multiple foci of isolated, acute consolidation, affecting one or more pulmonary lobes.