Macrophages are crucial components of the immune system and play a critical role in the initial defense against pathogens. They are highly heterogeneous and plastic and can be polarized into classically activated macrophages (M1) or selectively activated macrophages (M2) in response to local microenvironments. Macrophage polarization involves the regulation of multiple signaling pathways and transcription factors. Here, we focused on the origin of macrophages, the phenotype and polarization of macrophages, as well as the signaling pathways associated with macrophage polarization. We also highlighted the role of macrophage polarization in lung diseases. We intend to enhance the understanding of the functions and immunomodulatory features of macrophages. Based on our review, we believe that targeting macrophage phenotypes is a viable and promising strategy for treating lung diseases.

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that poses a serious threat to the global pig industry. Sichuan Province is one of the largest pig breeding provinces in China. There is a lack of reports on the continuous surveillance and systematic analysis of prevalent strains of PRRSV in Sichuan Province in recent years. To fill this gap, a total of 539 samples were collected from 13 breeding regions in Sichuan during 2012–2020. The detection result showed that the positive rate of PRRSV was 52.32% (282/539). The ORF5s and Nsp2 were obtained and further analyzed, with Chinese reference strains downloaded from the GenBank. Phylogenetic analysis showed that the PRRSV strains sequenced in this study belonged to PRRSV-1 and PRRSV-2 (lineage 1, 3, 5 and 8). In total, 168 PRRSV-2 strains were selected for ORF5 analyses, and these strains were classified into sub-lineage 8.7 (HP-PRRSV), sub-lineage 5.1 (classical PRRSV), sub-lineage 1.8 (NADC30-like), sub-lineage 1.5 (NADC34-like) and sub-lineage 3.5 (QYYZ-like), accounting for 60.71% (102/168), 11.31% (19/168), 18.45% (31/168), 2.97% (5/168) and 6.55% (11/168) of the total analyzed strains, respectively. The Nsp2 of identified PRRSV strains exhibited a nucleotide identity of 44.5–100%, and an amino acid identity of 46.82–100%. The ORF5 of the identified PRRSV strains exhibited a nucleotide identity of 81.3–100%, and an amino acid identity of 78.5–100%. A sequence analysis of ORF5 revealed that the mutation sites of GP5 were mainly concentrated in HVR1 and HVR2 and the virulence sites. In summary, the HP-PRRSV, NADC30-like PRRSV, Classic-PRRSV, QYYZ-like PRRSV, NADC34-like PRRSV and PRRSV-1 strains exist simultaneously in pigs in Sichuan. NADC30-like PRRSV was gradually becoming the most prevalent genotype currently in Sichuan province. This study suggested that PRRSV strains in Sichuan were undergoing genomic divergence.

Porcine astrovirus (PoAstV) is widely distributed worldwide, and is highly prevalent among piglets with or without diarrhea, existing as at least five distinct lineages (PoAstV1–PoAstV5) within the genus Mamastrovirus. However, our knowledge of the diversity and epidemiology of PoAstV in China is limited. In this study, fecal samples from 21/120 (17.5 %) domestic pigs, including 18/100 (18 %) diarrheic and 3/20 (15 %) healthy pigs, and from 1/9 (11.1 %) healthy wild boars tested in Sichuan Province were positive for PoAstV on reverse transcription–PCR. Of the 22 positive samples, 13.6 % were positive for PoAstV only, whereas 40.9 % also contained Porcine epidemic diarrhea virus (PEDV), 22.7 % also contained porcine group A rotavirus (PRoVA), and 22.7 % also contained PEDV and PRoVA. A phylogenetic analysis of the RdRp gene revealed genetic heterogeneity among the PoAstV sequences and two lineages were detected in this study, with PoAstV-2 predominant. PoAstV-5 was detected in wild boars for the first time. PoAstV infections exist in Sichuan Province regardless of the disease status in the pig population, either alone or in combination with other enteric viruses, and may be associated with diarrhea.

Porcine cytomegalovirus (PCMV) is an immunosuppressive virus that mainly inhibits the immune function of the macrophage and T-cell lymphatic systems, and has caused huge economic losses to the porcine breeding industry. Molecular epidemiological investigation of PCMV is important for prevention and treatment, and this study is the first such investigation in Sichuan Province, Southwest China. A PCMV positive infection rate of 84.4% (865/1025) confirmed that PCMV is widely distributed in Sichuan Province. A phylogenetic tree was constructed based on the PCMV glycoprotein B gene ( gB ) nucleotide and amino acid sequences from 24 novel Sichuan isolates and 18 other PCMV gB sequences from Genbank. PCMV does not appear to have evolved into different serotypes, and two distinct sequence groups were identified (A and B). However, whether PCMV from this region has evolved into different genotypes requires further research. Analysis of the amino acid sequences confirmed the conservation of gB , but amino acid substitutions in the major epitope region have caused antigenic drift, which may have altered the immunogenicity of PCMV.

We confirmed infection with influenza A(H1N1)pdm09 in giant pandas in China during 2009 by using virus isolation and serologic analysis methods. This finding extends the host range of influenza viruses and indicates a need for increased surveillance for and control of influenza viruses among giant pandas.