To Evaluate Safety, Tolerability, PK/PD & Food Effect of Single/Multiple Oral TUL321 Capsules in Healthy Participants.

Inclusion Criteria:

1. Participants can communicate well with investigators, fully understand the study, volunteer to take part, comply with all study requirements, and sign written informed consent before study procedures.
2. Age 18-45 years (inclusive) at informed consent, male or female.
3. Weight ≥50.0 kg for males, ≥45.0 kg for females; BMI 19.0-26.0 kg/m² (inclusive).
4. Female participants with child-bearing potential, and male participants whose partners have child-bearing potential: no pregnancy, sperm or egg donation from consent to 3 months after last dose, and willing to use study-required contraception.
5. For MAD-only participants: receive ACYW135 meningococcal vaccine and pneumococcal vaccine at least 14 days before first dose. No re-vaccination is needed if pneumococcal vaccine was given within 5 years, or ACYW135 meningococcal vaccine within 3 years prior to first dose.

Exclusion Criteria:

1. Suspected or confirmed allergy to investigational product or its similar components; or history of multiple drug/food allergies.
2. Past history of tuberculosis infection or active tuberculosis at screening.
3. Known or suspected history of immunodeficiency, inherited or acquired complement deficiency.
4. Confirmed active systemic bacterial, viral or fungal infection within 2 weeks before screening.
5. History of confirmed encapsulated bacterial infection within 6 months before screening, including but not limited to meningococcus, streptococcus pneumoniae, Haemophilus influenzae type b.
6. Clinically significant abnormal findings in laboratory tests, physical examination, vital signs, ECG, chest X-ray or abdominal ultrasound at screening.
7. QTcF (Fridericia correction) ≥450 ms at screening; or other risk factors for torsades de pointes (TdP), such as heart failure, hypokalemia, hypomagnesemia, family history of long QT syndrome.
8. eGFR <90 mL/min/1.73 m² (calculated by CKD-EPI formula) at screening.
9. Positive for HBsAg, anti-HCV, anti-HIV or syphilis-specific antibody at screening.
10. Received other vaccines not specified in the protocol within 1 month before screening, or plan to receive such vaccines during the study.
11. Participated in another interventional clinical trial within 3 months before screening (excluding subjects who only completed screening without enrollment, or enrolled but did not receive study treatment).
12. Average daily cigarette consumption >5 cigarettes within 3 months before screening.
13. History of drug/substance abuse within 6 months before screening, or positive drug abuse screening test.
14. Chronic constipation or diarrhea, or other conditions judged by investigator to interfere with fecal sample collection.
15. Required or plan to perform heavy physical labor or strenuous exercise during study participation.
16. Pregnant or lactating women, or women of child-bearing potential with positive pregnancy test at screening.
17. Acute illness or concomitant medication occurs from screening to pre-first-dose.
18. Cannot tolerate high-fat meal (applies only to subjects in the food-effect sub-study).
19. Difficulty swallowing, intolerance to venipuncture, or history of needle-syncope or blood-syncope.
20. Investigator judges that the subject is unsuitable for this study for any other reason.