Recall that bacteria (as a rule of thumb) elicit a neutrophilic inflammatory response. Here you can see the alveolar air spaces are full of PMNs as well of exsanguinated RBCs. It shouldn't surprise you then that hemoptysis (coughing up blood) can be a symptom of pneumonia. Notice that the interstitial space is left relatively normal.
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PMNs only live for 2 or 3 days. So (although you may not be able to make the distinction at this magnification) macrophages have replaced the PMNs. At the same time, the alveolar exudate has become fibrotic. This complication of lobar pneumonia is called "organizing pneumonia."
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Viral pneumonias manifest themselves in the interstitium rather than the alveolar air spaces. Notice that the interstitial space is greatly expanded with lymphocytes while the alveolar spaces are relatively normal. Does it make sense to you that viral pneumonias are usually less problematic than bacterial pneumonias? A common complication of viral pneumonia, however, is a secondary bacterial superinfection.
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